38

CHAPTER 2

LITERATURE REVIEW

2.1 MULTICLASS CALL ADMISSION CONTROL

TECHNIQUES IN W-CDMA

Huan Chen et al (2002) have proposed a call admission control

(CAC) scheme which gives preferential treatment to high priority calls, such

as and off calls, by pre-reserving a certain amount of channel margin against

the interference effect. It is called the interference guard margin (IGM)

scheme. The amount of guard margin is determined by the measurement

performed by the Resource Reservation Estimation (RRE) module in base

stations. Each RRE module dynamically adjusts the level of guard margin by

referencing traffic conditions in neighbouring cells based upon user’s

requests. A comprehensive service model is adopted to accommodate the

scenario of multiple services supported in the W-CDMA system. The service

model of consideration includes not only mobile terminal’s service rate

(source rate) but also different levels of priorities, mobility and rate adaptively

characteristics.

Their scheme has a dynamic call admission control based on two

concepts. First, a certain amount of interference-based guard margin (IGM) is

pre-reserved for the use of high priority calls. The amount of IGM is

dynamically adjusted by the resource reservation estimation module. Second,

the load curve is used to estimate the load increase as well as the interference

increase.

39

The concept of a guard margin illustrates, a new call to be admitted,

the total interference level should not exceed the upper bound of the

interference with threshold Ith that the system can tolerate. In addition to the

constraint of I’th, a lower priority call should comply with the augmented

constraint Ith. The margin between Ith and I’th is exactly the guard margin,

which provides the preferential treatment to high priority calls by limiting the

access to the low priority calls.

When a mobile terminal (MT) moves toward cell boundaries, the

neighbouring base stations (BS) receive stronger signal from it. Each of the

BS in the neighbouring cell will send messages to the main traffic switching

office (MTSO) to register itself as a handoff candidate for MT. The handoff

candidate registration (HCR) table is used in MTSO to maintain the

registration record and to inform the MT about where to handoff when its

signal fades. This table also provides very useful information to estimate

future handoff calls for a given cell. Before admitting a new or handoff call, j,

in a cell, dynamic resource reservation estimation scheme estimates the

interference guard margin IGM based on a weighted sum of estimated

minimum interference-increments according to the traffic profile for each

neighbouring active calls. In the CAC algorithm there are three types of

mobility, i.e. high, moderate and low mobility’s, are considered. By assigning

1, 2 and 4 units of speed for moderate and high mobility traffics, respectively.

The proposed CAC algorithm implies that a high speed MT is more likely to

handoff into the current cell even though it is farther away with respect to a

BS in comparison with a low speed MT.

The features of the proposed dynamic resource management are

summarized below:

40

Supports multiple service rates which are suitable for 3G

system such as wideband-CDMA (W-CDMA).

Supports rate adaptive characteristics for multiple services

with flexible QoS guarantees.

This scheme employs resource reservation estimation process

to adjust the level of reserved resources dynamically by

referencing the traffic condition in the neighbouring cells.

Bridges two concepts, guard channel (GC) and load curve

(LC) to provide the preferential treatment for high priority

calls.

Traffic mobility is considered in system model to achieve

better resource estimation results.

The system utilization is higher for traffic with the rate-adaptive

capability than that without the rate-adaptive capability under heavy traffic

loads. This can be explained by the fact that the system can provide calls with

a degraded service in terms of lower bandwidth when the system is congested,

thus increasing the overall system utilization. The use of weighting factor on

IGM increases the system utilization at risk of blocking more handoff calls.

Young-Long Chen et al (2007) have proposed a novel approach

which combines the CAC and power control mechanisms and operates in a

centralized control manner. The essence of the proposed centralized call

admission control (CCAC) scheme is to combine the two mechanisms and to

treat the call admission decision as an eigen-decomposition problem. In the

proposed approach, a new call is accepted only if the quality-of-service (QoS)

requirements of all the active links in the network can still be maintained. In

41

order to reduce the computational complexity of the eigen-decomposition

problem, they have proposed an additional scheme which uses a norm

operation rather than direct computation.

In their algorithm, it is assumed that all of the link gains between the

new call and the various base stations in the network can be estimated exactly

from the pilot signals broadcast during call setup initiation. Therefore, the

interference produced by the new call can be precisely predicted. When a new

call arrives, the decision to admit or reject the call is made depending on

whether or not there exists a power vector P which can guarantee every user’s

QoS requirement. The corresponding decision-making problem is formulated.

The QoS requirement is defined in terms of the bit error rate (BER) or the

frame error rate (FER). It is assumed that the BER or FER requirements can

be mapped into an equivalent SIR requirement for the modulation scheme.

Hence, when a new call arrives, it will be accepted only if the formulated

conditions are satisfied.

Malarkkan et al (2006) have presented functioning of call admission

control and resource reservation method based on the mobility of the users in

W-CDMA cellular systems. In order to assure the handoff dropping

probability, the mobility of the user was calculated based on a realistic

mobility model. The mobility calculation scheme was used to quote the set of

candidate cells into which the mobile may move in the near future and

calculates the similar value for each candidate cell.

The capacity of a CDMA system is limited by the total interference

it can tolerate, which is called the interference-limited system. Users with

different traffic profiles and attributes, such as the service rate, the signal-to-

Interference ratio (SIR) requirement, media activity, etc., different amount of

interference has been introduced to the system.

42

Malarkkan et al (2006) have analysed Fuzzy based Call admission

control scheme. They considered that the mobility information of the new

user requesting connection and already existing users, the type of service

request (real time or non-real time) and the load factor which is calculated

from the intra-cell interference and the inter-cell interference at the base

station. The QoS requirement of the non real time traffic is reduced to

accommodate more number of real time traffic users to improve the

performance of the admission control scheme.

In the Fuzzy logic a set is defined without a crisp boundary. The

transition from “belong to the set” to “not belong to the set” is gradual, thus

representing the truth grade related to the definition of the concept. This

smooth transition is characterized by the so-called ‘Membership Functions’

that give set flexibility in modelling commonly used linguistic expressions,

like “the temperature is hot” or the “weather is warm”. A Fuzzy System

consists of a Fuzzifier, an Inference Engine, a Fuzzy Rule Base and a

Defuzzifier. The Fuzzifier transforms the values of the input parameters into

the fuzzy linguistic terms through a set of Membership Functions. These

fuzzy linguistic terms are the inputs of the Inference Engine, which will

perform the logic inference according to the Fuzzy Rule Base. The Fuzzy

Rule Base is constructed by the expert knowledge of the phenomenon

(admission control). The Defuzzifier converts the results of the inference into

the usable values for admission decisions.

The Fuzzy Reasoning is, also known as “approximate reasoning”, it

is an inference procedure that derives conclusions from a set of fuzzy rules

and known facts. It can be divided into four steps:

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Degrees of compatibility: compare the known facts with the

antecedents of fuzzy rules to find the degrees of compatibility

with respect to each antecedent Membership Function.

Firing strength: combine degrees of compatibility with

respect to antecedent Membership Functions in a rule using

fuzzy AND or OR operators to form a firing strength that

indicates the degree to which the antecedent part of the rule is

satisfied.

Qualified induced consequent Membership Functions:

apply the firing strength to the consequent Membership

Functions of a rule to generate a qualified consequent

Membership Function.

Overall output Membership Function: aggregate of all the

qualified consequent Membership Functions to obtain an

overall output Membership Function.

Bazil Taha Ahmed et al (2008) have specified the uplink capacity

and the interference statistics for a W-CDMA 3-D Air-to- Ground (AG)

cellular like network assuming imperfect power control and finite transmitted

power. The free space model of propagation was used to calculate the

intercellular interference. The uplink capacity has been considered for various

frequencies and situations. It has been shown that the effect of rain was to

reduce the uplink capacity and the maximum permissible cell radius. Also it

was shown that, the frequency of operation should be lower or equal to 2

GHz. For a frequency of operation of 2 GHz, the cell capacity can reach 70

voice users or 46 data users when the cell radius is 320km. The new

contribution of their work was the study of the effect of an imperfect power

44

control and the finite transmitted power on the uplink capacity of the Air-

Ground system for various values of outage.

Seong-Jun Oh et al (2000) have studied the radio resource allocation

problem of distributed joint transmission power control and spreading gain

allocation in a DS-CDMA mobile data network. The network consists of K

base stations and M wireless data users. The data flows which are produced

by the users are considered as best-effort traffic, in the sense that there are no

pre-specified restrictions on the quality of the radio channels. They are

interested in designing a distributed algorithm that attains maximal (or near-

maximal in some reasonable sense) aggregate throughput, subject to peak

power constraints.

Jyoti Laxmi Mishra et al (2007) have evaluated various types of call

admission control algorithm. The objective of their research was to improve

the same algorithm with multiclass users and multiservice using fuzzy logic.

El-Dolil et al (2008) have examined the trade-off in the uplink

direction using power-based Multi-Cell Admission Control (MC-AC)

algorithm. Multimedia services were measured with different QoS

requirements. Different traffic situations were also considered. Their

simulation results exposes that MC-AC algorithms has many advantages over

single cell admission control in terms of overall constancy of the system and

total system throughput.

In this system, to investigate the performance of multi-cell

admission control they have developed a model. This model is used when

heterogeneous traffic is considered. Their results proved that MC-AC

algorithm has many advantageous over SC-AC. It has more advantage in

terms of dropping probability, network stability, and total system throughput.

They have examined the trade-off between the dropping and blocking. As per

45

their system dropping an ongoing call is more annoying than blocking a new

one. Call dropping probability can be lowered without much increase in

blocking probability. Both homogenous and heterogeneous traffic are

considered in this model. They have achieved more capacity gain under

heterogeneous (hot around) traffic distribution. Their results show that high

bit rate services suffer from both higher blocking and dropping probabilities.

Andrej Husar et al (2003) have presented a synopsis for call

admission control schemes, which are a part of radio source management

which plays a vital role at user admission into the system. They have also

explained some admission schemes into the system and also they have

compared their performance.

In their scheme the call admission control performed only, if

required power control is achieved. Otherwise it will reject the call. They

have proved that the dropping probability is less than the quality threshold.

And it keeps the admitted load as high as possible.

2.2 ADAPTIVE SCHEDULING TECHNIQUES IN W-CDMA

Salman AlQahtani et al (2007) have proposed and analyzed an

efficient uplink-scheduling scheme in case of Radio Access Network (RAN)

sharing method. With reference to this new scheme as Multi-operators Code

Division Generalized Processor sharing scheme (M-CDGPS). It employs both

adaptive rate allocation to maximize the resource utilization and GPS

techniques to provide fair services for each operator.

The CDGPS discipline is adapted and extended in order to design a

new high performance GPS based scheduling scheme which can effectively

control the shared resources among W-CDMA multi-operators in an efficient

and fair manner. Efficiency means higher system utilization and fairness

46

means that each operator is guaranteed at least a capacity equals to its

capacity share specified in the SLA. Therefore, a multi-operator CDGPS (M-

CDGPS) rate scheduling scheme for the uplink W-CDMA cellular network is

designed and analyzed.

Their scheme employs both adaptive rate allocation to maximize the

resource utilization and M-CDGPS to provide fair services for each operator.

The resource allocated to each operator session is proportional to an assigned

weight factor as per the SLA specification. After the initial allocation of the

allotted capacity, M-CDGPS scheme uses the CDGPS service discipline to

dynamically schedule the assigned channel rates of one operator among the

traffic classes within that operator independently. Moreover, the system

performance measures in terms of bounded delay and buffer size are also

derived using the GPS performance model.

They have compared the performance between static and adaptive

M-CDGPS. They have compared both scheme in terms of system throughput

and delay. They have designed a system with three operators. They have

fixed same traffic load for two operators which is fixed one and they have

fixed different traffic load for the third operator. They have used a long range

of offered traffic. By that they have examined the system behaviour at low

and high traffic loads. They have shown that the throughput of adaptive rate

M-CDGPS is higher in case of using adaptive rate because of utilizing the

residual resources of other operators. Hence the system throughput increases.

They have also shown that the throughput is linearly increases as the offered

traffic increase. They have proved that, when the saturation point is reached,

the flow of third operator who is fixed with different traffic load is limited to

its minimum assigned rate.

47

Nidhi Hegde et al (2006) have designed a resource sharing of BE

applications with the RT applications in W-CDMA networks. Both the types

of traffic have flexibility to adapt the obtainable bandwidth but not like the

BE traffic. RT traffic requires strict minimum bounds on the throughput. They

have examined the performance of both BE and RT traffic and examined the

effect of reservation for some portions of the bandwidth for the BE

applications. Also they have presented a novel capacity definition associated

to the delay of BE traffic and showed how to calculate it.

They have considered best-effort (BE) traffic sharing the network

resources with real-time (RT) applications. They have shown that the BE

applications can adapt their instantaneous transmission rate to the available

one. Their meaningful QoS is the average delay. They have defined delay

aware capacity. Which is defined as the arrival rate of BE calls. Their system

can handle the expected delay of BE calls bounded by a given constant. They

have computed blocking probability of the RT traffic having an adaptive

Grade of Service (GoS) and the expected delay of the BE traffic for an uplink

multi-cell W-CDMA system. Thus their system yields the Erlang capacity for

former requirement and the delay capacity for the latter requirement.

They have assumed that RT traffic is subject to Call Admission

Control (CAC) in order to guarantee the minimum rates for accepted RT calls.

This implies that RT traffic may suffer rejections whose rate is then an

important QoS for such applications. In contrast, Best effort (BE) applications

can adapt their transmission rate to the network’s available resources and is

therefore not subject to CAC. The relevant QoS measure for BE traffic is then

the expected time delay of a call in the system.

They have considered BE traffic sharing the network resources with

RT applications. Their aim is to compute both the blocking (or rejection)

probability of the RT traffic as well as the expected delay of the BE traffic for

48

an uplink multi-cell W-CDMA system. RT calls need a minimum guaranteed

transmission rate, they are assumed to be able to adapt to network resources in

a way similar to the BE traffic. They have proved that duration of BE calls

depends on the dynamic rate assignment. They have proposed a probabilistic

model that takes these features into account and enables to compute the

performance measures of interest. And they have computed the blocking

probabilities and the average throughput per RT calls, the expected average

number of RT and BE calls in the system, and the expected delay of BE call.

They have modelled a resource sharing of BE applications with RT

applications in W-CDMA networks. Both type of traffic have flexibility to

adapt to the available bandwidth but unlike BE traffic, RT traffic requires

strict minimum bounds on the throughput.

Rekha Patil et al (2008) have proposed a Scheduling scheme which

aims to allocate the wireless channel to contending nodes. Through that they

reduced multiple access interference. At the same time each node is

guaranteed a minimum acceptable level of performance in terms of metrics

such as data rate, delay, probability of error etc.

Their scheduling algorithm admits the transmissions of static as well

as mobile users of multi service classes, in order to eliminate strong levels of

interference. That interference cannot be overcome by power control. They

have given priority for the mobile users when determining the admissible set

of users.

Remco Litjens et al (2002) have evaluated data and voice calls in

UMTS network. They have evaluated several scheduling scheme with

dynamic adaptation of transport channel rates. The have examined the

function of scheduling scheme according to the sharing of limited resources

for varying number of voice calls. It gives different traffic load to the

49

scheduling scheme. Based on the certain fairness objective they have

distributed the resources according to present load of a particular cell. They

have evaluated the analytical performance of each scheduling scheme.

They have evaluated the performance of the scheduling scheme in

the downlink of UMTS network. The network consists of integrated and

prioritized speech data and voice calls. They have derived closed form of

expression to apply optimal power for multiplexing of data transmission.

Along with this, it protects the performance of voice calls. They have

provided numerical examples for performance improvement of data and voice

calls by the utilization of scheduling scheme. The have assigned a minimum

power for voice and data calls to evaluate the performance and resource

sharing capabilities of UMTS network.

Leonardo et al (2003) have analyzed and presented a model trade-

off between the QoS metrics, blocking and dropping probability. They have

analyzed obtained performance is under different points conditions and they

exposed required aspects. They have analyzed known algorithms, in terms of

fairness and generality of the performance. They have taken realistic models

for mobility, data rate and discontinuous transmission (DTX) into account..

Their proposed approach to CAC is aware of mobility differences

among users. The mobility difference of the user is easily tracked by the base

stations. Their results proved that traditional approaches will give unfairness

results if users have different mobility patterns coexist in the same system.

Their Mobility-aware Interference-based CAC (MICAC) can provide much

better fairness performance compare to all other traditional users.

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They have modelled Call Admission Control instantaneous

threshold algorithms for 3G. The Mobility aware Interference based Call

Admission Control improves the performance of network. It is used in

instantaneous heuristic evaluation of the network. Their results may be

globally good, improvement under the aspect of fairness may still be

necessary. They have tested different systems under the aspects of sensitivity

to their parameters and fairness. They have identified that the performance

can be improved by a better model of the drop policy. In drop policy along

with mobility class, global blocking and dropping probability, but even the

behaviour with respect to each mobility class is considered for evaluation.

Jean Marc Kelif et al (2005) have considered W-CDMA system

with two types of calls. They are, real time (RT) and non-real time (NRT)

calls. Real time calls have dedicated resources, and data. Non-real time (NRT)

calls are treated using a time-shared channel (such as the HDR or the

HSDPA). They have reserved some resources for the NRT. The NRT further

assign the given resources to RT. They have controlled the grade of service

(GOS) of RT to handle and admit more RT calls during congestion period. It

degrades the existing user to provide service to more RT calls. They have

considered both uplink and downlink. Through this they have examined the

blocking probability and sojourn time of NRT calls. They have tested further

the conditional expected sojourn time of a data connection, size and the state

of the system. They have examined and created a framework to handle

handover calls.

They have further multiplexed NRT calls using time. It avoids the

amount of interference and increasing the available average throughputs. This

51

kind of multiplexing is used in High Speed Downlink Packet Access

(HSDPA). It is a high speed downlink data channel.

They have proposed a simple model to analyze the capacity

requirement of a call of given class. It is performed only when the call of class

uses the given grade of service (transmission rate). They have proposed a

control policy to combines admission control together with a control of the

grade of service (GoS) of real-time calls. They have computed the Key

performance measures by quasi-birth-and-death (QBD) process. They have

obtained the call blocking probabilities and expected transfer times, already

available for the uplink case. They have further obtained another important

performance measure for both uplink and downlink. That is expected transfer

time of a file conditioned on its size. They have analyzed the influence of the

control parameters on these performance measures. They have further

examined the model to handle handover calls.

Remco Litjens et al (2002) have evaluated data and voice calls in

UMTS network. They have evaluated several scheduling scheme with

dynamic adaptation of transport channel rates. The have examined the

function of scheduling scheme according to the sharing of limited resources

for varying number of voice calls. It gives different traffic load to the

scheduling scheme. Based on the certain fairness objective they have

distributed the resources according to present load of a particular cell. They

have evaluated the analytical performance of each scheduling scheme.

They have evaluated the performance of the scheduling scheme in

the downlink of UMTS network. The network consists of integrated and

prioritized speech data and voice calls. They have derived closed form of

expression to apply optimal power for multiplexing of data transmission.

52

Along with this, it protects the performance of voice calls. They have

provided numerical examples for performance improvement of data and voice

calls by the utilization of scheduling scheme. The have assigned a minimum

power for voice and data calls to evaluate the performance and resource

sharing capabilities of UMTS network.

2.3 POWER CONTROL TECHNIQUES IN W-CDMA

Dejan Drajic (2002) has formulated some adaptive technique to

enhance power control technique in W-CDMA. The fast power control for

downlink is a very important part of the system. The aim is to keep the

received power per bit at a satisfactory level. It is well known that the power

control can be very efficient when the receiver velocity is relative small. On

the other hand, turbo codes with long inter-leaver are expected to combat

successfully with short deep fades appearing during the fast moving of the

receiver.

In CDMA system power control (PC) has a strong effect on the

interference experienced by the receiver, and hence it directly affects its

performance. The compensation of fading channels and changes in the

transmitted powers of interfering users are recognized as the main

characteristics of power control. However, it might cause problems on the

adaptation of equalizers. The power control in W-CDMA is SIR (or SINR)

based. In the model, due to exceptional complexity of such an approach, a

simplified model based on signal-to-noise ratio (SNR) was implemented.

Here, perfect knowledge of channel is assumed and powers of other

interfering users and CPICH are held constant. Also, the power control model

compensates only for the fading channel of the desired user. The

characteristics and parameters of model are: the power range of desired user is

limited ±10dB around nominal Eb/N0 level, and the received Eb/N0 is

53

averaged over last two pilot symbols in a slot, and compared to the nominal

Eb/N0. The transmitted power is changed 1dB step for the next slot to

compensate for the difference in Eb/N0 within limit of power range. In the

generation of power control command for the next slot, the transmitted power,

channel coefficients and noise power are known, and detection of power

control commands in base station is assumed to be error free.

Siamak Naghian et al (2002) have proposed a novel dynamic step

size power control method to improve the performance of UMTS/W-CDMA

cellular system. The proposed method utilizes dynamic step-size power

control commands, received SIR/power, and mobile handset location

assistance data. Furthermore, dynamic inter-operation between the power

control, admission control, and handoff control is evolved to improve the

convergence of the proposed power control mechanism. Based on the output

of this interoperability, a multi-step transmit power edge setting is proposed.

In the uplink power control, on the network side, the radio access

control and the base station are involved in the controlling part of the power

adjusting process. The Admission Control and the Power Control entities of

the radio access controller set the signal quality targets, which includes

SIR_max, SIR_opt_max, SIR_opt_min, and SIR_min. This can be based on

the traffic information available in AC, signal strength, SIR, access priorities,

location assistance information, and so on.

First, the mobile station receives the power control commands from

the base station. It registers the forthcoming power control command into the

command bit register. The change history can also be stored there, including

data on the latest power control commands, step-sizes, and possibly the

handset coordinates. The mobile station goes through the power control

command values, step-sizes, and possibly location assistance data, included in

the change history. If the power control command or step-size stream is even,

54

meaning that the power level is not radically changed but is kept stable, then

there is no considerable need for changing the transmit power.

If the power control command or step-size stream is not even, the

process advances to the step, where it is checked whether the power control

command stream is uneven, in other words if only one set of the power

control commands is repeated often. In that case the larger step-size could be

considered to compensate the variations of the transmit power.

If the power control command or step-size stream is not even nor

uneven but they are repeated irregularly, then the process advances directly to

the step where a fast power control without delay takes place. Location-aware

mobile station is able to predict the possible environmental changes, which

may affect the radio channel and avoid phenomena such as “corner effect”

when making the power control decision.

Subba Rao et al (2011) have proposed an adaptive power control

mechanism for multimedia traffic in W-CDMA networks. Their algorithm

uses two most recent Transmit Power Control (TPC) commands to compute

the Adaptive Factor (AF) based on a predefined Adaptive Control Factor

(ACF). With introduced another parameter, Power Determining Factor (PDF)

based on the data traffic rate to determine the power. Based on this parameter,

the power is increased or decreased. Depending on the traffic rate, the PDF

factor is updated i.e., if the observed traffic rate is high, then it will increase

the parameter and subsequently increases the power and if it is low, then the

parameter will be decreased and correspondingly the power also.

The aim of a power control procedure is to ensure an adequate SIR

for all mobiles in a system by a simple algorithm. The algorithm requires

feedback information from the receiver and based on that, the transmitting

power is adjusted at transmitter side. The information regarding the feedback

55

is delivered by means of the feedback information. The bandwidth of the

feedback is expensive and so the amount of information required by the

procedure must be kept minimal.

There are outer and inner loop power controls. The outer-loop

power control is performed by Radio Network Controller (RNC). Based on

some particular measured parameters such as BLER (Block Error Rate), the

outer loop power control adjusts the SIR target. The required BLER depends

on radio conditions and service types. According to the conditions and service

types, the individual SIR target of each mobile will be set. The requirement of

SIR target will be higher if a mobile moves quickly resulting in rapid change

in radio channel and vice versa. In addition, different service types require

different BLER. The SIR targets of data services are higher than the voice

service as the data service requires lower BLER than voice services. The

frequency of SIR target updating is 10-100 Hz.

Inner loop power control mechanism adjusts the transmitted power

to maintain the received SIR equal to the SIR target at the receiver. In 3GPP

specifications, each W-CDMA frame of length 10ms consists of 15 time slots

and each of which consists of one bit of the power control command called

“Transmit Power Control” or TPC. TPC is a command, which increases or

decreases the transmitting power. The transmitter will be controlled to

increase OR decrease the transmit power, so that the power will always be

oscillated even if the received SIR is close to the SIR target. The step size will

be increased if same TPC commands are detected or else the updated step is

very large, the step size will then be decreased.

The power control step size is adapted by multiplying a factor called

Adaptive Factor (AF) with the fixed step size. This factor will be updated

according to received TPC commands. The proposed algorithm increases the

step size i.e. AF when the mobile detects the same sequence of TPC. The

56

same sequence of TPC commands will occur when rapid changes of power

are required, such as when the radio channel condition variants rapidly and

continuously. The proposed algorithm uses two most recent TPC commands

to compute the AF based on a predefined ACF. The ACF is a constant chosen

by the networks.

In their proposed algorithm, they have introduced a new parameter,

Power Determining Factor (PDF) based on the data traffic rate to determine

the power. Based on this parameter, value is determining whether the power is

increasing or decreasing. Depending on the traffic rate, the PDF factor is

updated. If the received message is HCM, then it will increase the parameter

and subsequently increases the power and if the message is LC, then the

parameter will be decreased and correspondingly the power also.

Ch. Sreenivasa Rao et al (2012) have proposed a power controlled

call admission control scheme for handoff in the advanced wireless networks.

The incoming call measures the initial interference on it and then the base

station starts transmitting the packets to the new call. The new call is rejected

when the interference reaches a threshold value. Whenever an existing call

meets the power constraint, the transmit power is decremented based on the

traffic class and incoming call obtains this information by monitoring the

interference received on it. The convergence of the power control algorithm is

checked and the power levels of all incoming calls are adjusted.

The power constraint for admitting a new call is determined using

the present uplink interference, increased uplink interference, and the target

threshold. The power decrement value is calculated for both the real-time

packets and the non-real time packets. Using this algorithm, the call

admission is processed based upon the power constraints.

57

The QoS Based Adaptive Admission Controller (QAAC) technique

measures the channel quality and separate queues for maintaining each class

of service. The basic concept of QAAC algorithm is to simultaneously

provide transmission priority and space priority for the data flows of the same

end-user. The algorithm tries to minimize the number of the sessions that are

blocked due to insufficient resources in the target network.

The power constraint for admitting a new call depends upon the

present uplink interference, increased uplink interference, and the target

threshold. When the target threshold exceeds the sum of the present uplink

interference and the increased uplink interference then the call cannot be

admitted.

Aguero et al (2009) have presented new methods to improve control

with respect to the strong non-linear effect. Therefore they have proposed

adaptive control architecture for inner loop power control, having three

degrees of freedom. Their three degrees of freedom were used to address

errors resulting from channel/interference variations, quantization of the

power increments and saturation of the power increments. They have also

added a simple adaptation mechanism to their design so that non-stationary

channel gain and interference models could be tracked. A disadvantage of

their adaptive scheme was that information about the channel interference

model has needed to be transmitted from the base station to the mobile unit.

They have proposed a novel architecture for inner loop power

control of CDMA cellular systems. This algorithm uses uplink of the W-

CDMA system as an example. These methods are of general validity for

power control of CDMA cellular systems. The architecture has three degrees

of freedom. They have developed this system to address simultaneously three

performance limiting factors. (i) the effect of SIR changes due to channel and

interference variations, (ii) the effect of quantization of the power increments

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and (iii) step size issues. In this scheme they have used simple adaptation

mechanism. Through simulation they have shown that the scheme

consistently working in other related architectures. They have shown that the

adaptation mechanism yields a globally stable closed loop system. The

performance of the proposed architecture is shown that it reduces the variance

of the control signal, prior to its quantization.

Markus Laner et al (2010) have analyzed the un-coded BER

parameter, with respect to its possible contribution to an improvement of the

uplink OLPC algorithm. Their research was performed by means of extensive

measurements in a live network which proved that the actual implemented

algorithm converged slowly. They have also founded that the reason was due

to the QoS estimated by CRC and as the un-coded Bit Error Ratio (BER) hold

information about the QoS, this parameter could be used to increase

convergence speed of their OLPC. They have also presented a statistical

model of the control path of the OLPC which considered the un-coded BER

information.

The have proved that large-scale measurements have shown that the

uplink OLPC algorithm in UMTS networks, has a convergence time in the

order of a short call duration. It cannot follows quickly changing SIR

demands of a user in movement. They have provided a detailed analysis of the

relations between target SIR, BLER, and un-coded BER for static and moving

users, respectively. Their results revealed that the un-coded BER can be used

to multiply the OLPC convergence speed. Further they have proposed a new

OLPC algorithm which makes use of this parameter. They have simulated

using different time with different kind of user to check SIR value. They have

checked the user in movement, static user and user with short duration call.

They have showed that the algorithm reduces the mean target SIR with

independent of the user mobility.

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Tajje-eddine Rachidi et al (2004) have presented a QoS aware

mechanism for power control and Handoff in 3G W-CDMA networks. They

have also presented two mechanisms named Quality of Service aware Power

Control (QaPC) and QoS aware prioritization of Handoffs (QaHO) which

were based on the class of service, bit rate and Service Degradation

Descriptor (SDD) as enabling QoS parameters. They have also obtained the

numerical results using a W-CDMA and UMTS compatible test bed which

showed that their proposed QoS aware mechanism significantly improved the

QoS contract upholding for premium mobile users, as well as increased

resource utilization, while improving the acceptance of soft handoffs.

In two phases the adaptation algorithm resolves congestion. In case

of congestion handling and in case of SHO admission these two phases are

applied differently. User Equipment (UE) contains a QoS profile as specified

by their QoS framework. Their profile comprises the required bit rate, traffic

class, and the Service Degradation Descriptor. They take values between 0

and 5 for SDD. The user with larger SDD value is considered as to degraded

or dropped. They have proposed two phases to perform this operation. They

are as follows,

The Degradation Phase

This phase is based on the service degradation descriptor. The active

connection which has highest SDD value is degraded based on their

bandwidth. In this phase they have degraded such connection with 384Kbps

bit rate requirement to 144Kbps. Similarly 144Kbps is swapped for 64Kbps,

and 64Kbps is swapped for 16Kbps. 2 Mbps and 16Kbps connections are not

degraded in their schema.

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The Dropping Phase

This phase is working based on willingness of the user. This phase

is invoked only when willingness received from the user. Then their

connections were degraded. After dropping the call congestion persists in this

phase.

2.4 INTERFERENCE REDUCTION TECHNIQUES IN W-CDMA

Derong Liu et al (2007) have presented a simple interference

cancellation technique for the downlink of wideband code division multiple-

access (W-CDMA) systems in multipath environment. With the same

knowledge required by a RAKE receiver, the present method acts as an

equalizer and cancels the interfering multipath signals from the received

signal to retrieve the orthogonality property of the received signal. The

present receiver has a simple structure and it has significant performance gain

against the RAKE receiver. In addition, the noise enhancement is negligible

when there is a line of sight path or the channel power delay profile has an

exponential decaying form.

In their work, a new technique for multiple access interference

(MAI) cancellation based on successive cancellation of interfering multipath

signals from the received signal is presented. Their method has the capability

to completely cancel the MAI with only a slight increase in complexity

compared to the conventional RAKE receiver. The three basic assumptions

often used in some literature under which the application of their method is

feasible include:

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There is a guard interval at the beginning of each transmitted

frame so that there is no interference between two consecutive

frames, though this guard interval may used for different

purposes;

The multipath delays are integer multiples of the chip interval,

this assumption is easily achieved by sampling the data in

multiple integer of the chip rate; and

There exists a line of sight path (a relatively strong first path),

or the channel power delay profile has an exponential

decaying form.

Pon Rattanawichai et al (2011) have presented the FPGA (Field

Programmable Gate Array) implementation of self interference cancellation

technique based on an adaptive LMS (Least Mean Square) algorithm. By

using the FPGA Virtex@6 HW module, the field data measured through a RF

repeater is adopted to improve a signal quality and to reduce oscillation of the

system due to the feedback interference signal coming from transmit antenna

of a W-CDMA radio repeater.

The main parts of their system are composed of:

“New Weight Vector” block: obtaining an internal value

named “Input Values” to be used further in the coefficients

update.

“ICS Input” block: buffering the input received signal in

FPGA after performing ADC conversion.

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“Filter Error Calculation” block: canceling the interference

feedback signal yF using the estimated feedback signal yE.

“ICS Output” block: buffering the cleaned output signal

before performing DAC conversion.

“Normalization” block: suppressing the amplitude signal to an

effectively sufficient level in order to accelerate the

convergence rate of the LMS algorithm.

Jraifi Abdelouahed (2012) has proposed the system in which, radio

frequency interference is caused by occupying exiting radio frequency

resource, improper configuration of network by different operators, cell

overlapping external interference sources and electromagnetic compatibility.

Mobile communication interference is common-frequency, adjacent-

frequency, out of band spurious emission, inter-modulation emission and

blocking interference. He has developed an analytical expression of the Signal

to Noise Ratio (SNR) which is used to predict some parameters. By fixing the

SNR to a specific value, he has extracted easily information on the optimal

numbers of users.

He has adopted a micro-zoning architecture to compute the (S/I)

ratio. This analytical result is used to predict the number of users per micro-

zones. This result is of crucial importance because it contributes positively in

improving the quality of services. Furthermore, if one success to integrate

some system parameters into the theoretical result then his approach could

also be used for other applications.

Anis Masmoudi and Sami Tabbane (2006) have proposed two

systems called uniform and non-uniform traffic environment in interference

of W-CDMA. It presents an analytical work which provides exact derivations

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of the general F-factor, CDF and PDF distributions laws, mathematical

expressions in W-CDMA systems with one interferer. Their approach doesn’t

depend on any assumption or values range. They have also investigated the

unequally-loaded cell case referring to the more general non-uniform mobile

distribution. They have proved that this model refines the planning process

and thus increase the quality and capacity of a cellular network.

In Uniform traffic distribution, all the cells are assumed to be

equally loaded, i.e. the traffic and users distribution are uniform within each

cell, allowing the deployment of a regular grid of base stations (BS) or nodes

B. Propagation conditions are assumed to be the same all over the studied

area. In such conditions, by considering a simplified scenario with only two

nodes B (one is the serving node B and the other is its neighbor interferer) –

the required transmitted powers for the two nodes B are the same. Therefore,

the power of both interfering and serving nodes B, really used, can be

mathematically simplified when calculating f-parameter which becomes

depending only on different path losses as expressed later in another node.

Total transmit power reflects the equally-loaded cell case, independently of

any power control on the downlink, considered as perfect in this modeling.

Thus, in each link, the transmitted power is the one needed to ensure to the

mobile the required quality corresponding to the received SIR (Eb/N0)

necessary for the used service. So, the downlink transmitted power to each

mobile is not constant since its position varies as well as the propagation

conditions from one mobile link to another.

Non-uniform traffic distribution occurs with non-uniform traffic

environments or at the borders of two different traffic environments (e.g.,

urban and sub-urban). Overloaded cells size will shrink (cell breathing

phenomena) compared to unloaded ones. The size reduction of the most

loaded cell of the network is due either to uplink capacity limitations or to

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downlink coverage limitation. The first case occurs when the overloaded cell

traffic density increases and reaches the uplink pole capacity limit. The

maximum number of users depends on many factors such as service type

mixture, required quality of service, traffic and service distribution, and the

maximum allowed uplink noise rise.

Their study is particularly useful for choosing the convenient value

of f-parameter to consider in the loading equations or in the generic downlink

SIR expression and suitable for input static simulations and thus an accurate

design of UMTS cellular networks in different load conditions. In fact, their

analytical approach gives accurate modeling of f-parameter distribution and

thus corrects values that should be used in simulations required for a

preliminary planning process both in equally and unequally-loaded cell cases.

Moreover, their study is not valid only for regular grid cells, but it applies also

to irregular networks which operators are trying to optimize. In fact,

unequally-loaded cells due to non-uniform users distribution and cell

breathing in W-CDMA networks are based on cells with different sizes, and

thus on irregular cell grid principle.

The analytical calculations performed are very long and not

straightforward even after simplification to one interferer. Here, the

calculations have not been done directly considering multiple interferers

because the sum distribution is not as trivial as it seems. The f-parameter PDF

expression with shadowing has also been established using convolution

product and has been plotted by simulations and differentiated with that

without shadowing in various propagation environments. Shadow correlation

has also been taken into account.

Maan Al-Adwany et al (2011) have proposed interference canceller.

In W-CDMA base station receiver, the BER can be considerably reduced by

using the proposed interference canceller. Initially, they have extracted the

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TDMA interference through the use of a low pass FIR filter. They have

constructed a threshold circuit to eliminate the residual W-CDMA signal that

passes with the extracted TDMA signal. Finally, they have also evaluated the

performance of W-CDMA uplink system for UMTS mobile communications.

The idea their proposed interference canceller is to extract the

TDMA interference through the use of a low pass FIR filter which is matched

to the TDMA bandwidth (2.048 MHz), and then subtract the extracted TDMA

signal from the received composed signal (TDMA+W-CDMA). Hence, it is

possible to get a W-CDMA signal with approximately no TDMA

interference.

The threshold circuit is used to eliminate the residual W-CDMA

signal which passes with the extracted TDMA signal. The filter has a cutoff

frequency of 2.048 MHz which is matched to the TDMA system bandwidth.

Also, when designing the filter, the group delay of the filter is to be taken into

consideration. It must not have a large group delay (group delay= {filter

order – 1}/2). In their design, they select a reasonable filter order of seven;

which gives a group delay of three sample periods.

Since the signal will suffer a group delay of three sample periods

when it passes through the designed FIR filter, this delay must be

compensated by adding a delay line (z-3) for the purpose of signals alignment.

Also, it is worthwhile to mention that all the delays and their compensations

are taken into account throughout the simulation.

Muhammad Suryanegara et al (2006) have examined the

interference on W-CDMA system that caused by CDMA2000 network. The

have used several scenarios and calculation models were applied to measure

impacts on uplink and downlink scheme. Their results showed that

interference from CDMA2000 influence W-CDMA performance

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significantly. Distance between coexistence terminals (MS and BS), their

number, and guard band frequency determined minimum allowed received

power at W-CDMA BS and SIR in W-CDMA MS, which lead to capacity

degradation.

They have examined the effect of adjacent channel interference on

the W-CDMA system uplink and downlink scheme. The have used 3G

coexistence network, the presence of CDMA2000 system influenced W-

CDMA as a environment to check the performance. They have shown that the

interference generated by CDMA2000 MS increased the minimum allowed

received power at W-CDMA BS. It leads to reduction of W-CDMA coverage

and cause a significant capacity loss. In downlink scheme, they have shown

that the interference due to CDMA2000 BS influenced the performance of W-

CDMA communication system which can be seen from significant reduction

of SIR value. The over all outcome of their experiment is effect of

interference depends on several factors including distance between W-CDMA

and CDMA2000 terminals (BS and MS), number of CDMA2000 MS,

interference power, and guard band frequency. They have used a guard band

to reduce the effect of interference.

2.5 GAP ANALYSIS

In 2002, Huan Chen et al (2002) have proposed a call admission

control (CAC) scheme which gives preferential treatment to high priority

calls, such as and off calls, by pre-reserving a certain amount of channel

margin against the interference effect. This is the interference guard margin

(IGM) scheme. In the dynamic IGM scheme, the resource reservation module

is used to dynamically reserve an interference margin for the use of potential

high priority calls by referencing the traffic condition and mobile users’

traffic profile in neighboring cells. Their fixed and dynamic IGM schemes

outperform the non-priority scheme in the overall objective function.

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In 2007, Young-Long Chen et al (2007) have proposed a novel

approach which combines the CAC and power control mechanisms and

operates in a centralized control manner. Their approach outperforms

conventional call admission methods both in terms of its blocking rate and its

outage rate. The main benefit of their proposed CCAC method is that it takes

the entire link conditions into account such that their minimum SIR

requirements are maintained when a new call is admitted.

In 2006, Malarkkan et al (2006) have analysed Fuzzy based Call

admission control scheme. The fuzzy approach can overcome measurement

errors; mobility and traffic model uncertainty, and avoid the requirements of

complex mathematical relations among various design parameters. The fuzzy

CAC scheme can achieve QoS satisfaction in terms of the outage probability,

and achieve lower new call blocking probability, lower handoff call dropping

probability when compared with the SIR based CAC schemes without fuzzy.

In 2007, Salman AlQahtani et al (2007) have proposed and analyzed

an efficient uplink-scheduling scheme in case of Radio Access Network

(RAN) sharing method. Their proposed adaptive rate MCDGPS scheduling

scheme improves both system throughput and average delays.

In 2002, Siamak Naghian et al (2002) have proposed a novel

dynamic step size power control method to improve the performance of

UMTS/W-CDMA cellular system. In their method, the multi-edge threshold

concept, dynamic step-size, power-control commands/steps-based history data

have been used. Their proposed dynamic step-size power control method can

be more efficient than a conventional one due to its capability to deal flexibly

with both slow and fast fading of the transmission signal of the W-CDMA

system. Also they have utilized the location information jointly to combat

transmit power deterioration.

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In 2004, Dejan Drajic (2004) has formulated some adaptive

technique to enhance power control technique in W-CDMA. They have

shown that the power control and channel coding complement each other

when mitigating the effects of fading. In CDMA system power control has a

strong effect on the interference experienced by the receiver, and hence it its

performance is directly affected.

In 2011, Subba Rao et al (2011) have proposed an adaptive power

control mechanism for multimedia traffic in W-CDMA networks. Their

power control algorithm reduces the power consumption of multimedia

traffic. They introduce a new parameter, Power Determining Factor (PDF)

based on the data traffic rate to determine the power. Based on this parameter,

they are determining whether the power is increasing or decreasing.

Depending on the traffic rate, the PDF factor is updated.

In 2012, Ch. Sreenivasa Rao et al (2012) have proposed a power

controlled call admission control scheme for handoff in the advanced wireless

networks. In their scheme, the hybrid priority queuing mechanisms for call

requests and efficient scheduling a power controlling mechanism have been

used in the handoff process. Their power control technique provides efficient

handoff in the 4G networks by not degrading the QoS parameters like

throughput and delay.

In 2007, Derong Liu et al (2007) have presented a simple

interference cancellation technique for the downlink of wideband code

division multiple-access (W-CDMA) systems in multipath environment. Their

method acts as an equalizer and cancels the interfering multipath signals from

the received signal to retrieve the orthogonal property of the received signal.

Their algorithm is not complex and does not consume much time since each

information bit can be detected after the interfering chip cancellation is done

in a bit interval. The simplicity of their algorithm with the perfect cancellation

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of MAI comes at the expense of noise enhancement. Although this noise

enhancement causes a loss of few dBs in SNR compared to the single user

system, the performance of the receiver, as the simulation results show, is

much higher than the RAKE receiver and is free from any error floor.

In 2011, Pon Rattanawichai et al (2011) have presented the FPGA

(Field Programmable Gate Array) implementation of self interference

cancellation technique based on an adaptive LMS (Least Mean Square)

algorithm. Their algorithm achieves a high efficiency and the similar

performance in comparison with the implementation result. By the FPGA

implementation, their designed technique provided more flexibility than

existing methods.

In 2011, Maan Al-Adwany et al (2011) have proposed interference

canceller. They have been shown that the W-CDMA and TDMA systems can

work in the same cell and hence, it is possible to increase the cell capacity as

the problem of cross interference between the two systems can be reduced

using the proposed interference canceller. In W-CDMA base station receiver,

the BER can be considerably reduced by using the proposed interference

canceller. On the other hand, in TDMA base station receiver, the effect of W-

CDMA interferers can be reduced by increasing the transmitted power of the

TDMA mobile station.