Radio Parameter Planning

Radio Parameter Planning

1

Radio Network Planning – Training Document

Radio Parameter PlanningRadio Parameter Planning


2

Contents

• Channel Planning

• CGI Planning

• Frequency Planning


3

Channel Planning

Physical timeslot = one burst (transmission quantum of GSM) = 156.25 bitsThe 156.25 bits are transmitted in 0.577ms

•Information (user data/voice or control/signaling messages)•Tail-bits to allow the signal level to rise to an amplitude-level from zero-level before sending actual information.Training sequence – some predefined bit-sequence, known to the receiving end, to help extract information bitsaccurately.Flag is relevant for TCH only.


4

• Normal burst : TCH, SDCCH, FACCH, SACCH • F burst : FCH• S burst : SCH• Access control burst : RACH and AGCH Note that the F and S bursts have the same length as a normal burst but a different internal structure, which differentiate them for normal bursts (synchronization)


5

Channel Planning


6

The Broadcast Control Channels are downlink only (base station to mobile) and comprise of the following: • BCCH carries info about the network, a mobiles present cell and the surrounding cells. It is transmitted continuously as its signal strength is measured by all mobiles on surrounding cells.

• The Synchronizing Channel (SCH) carries information for frame synchronization and Base Station Identity Code (BSIC).

•The Frequency Control Channel (FCCH) provides information for carriersynchronization.

BCCH Group

Channel Planning


7

The Common Control Channel Group comprises of the following: •Random Access Channel (RACH) is the uplink used by mobiles to gain access to the system.

•Paging Channel (PCH) is used by the system to call a mobile.

•Access Grant Channel (AGCH) operate in the downlink direction. The AGCH is used to assign resources to the MS, such as a SDCCH.

Note that the PCH and AGCH are never used at the same time.

CCCH Group

Channel Planning


8

DCCH Group

Dedicated Control Channels are assigned to a single mobile for call set-up andsubscriber validation. DCCH comprises of the following:

•Standalone Dedicated Control Channel (SDCCH) which supports the transfer ofData to and from the mobile during call set-up and validation.

•Associated Control Channel. - This consists of Slow ACCH which is used for radio link measurement and power control messages. - Fast ACCH is used to pass event type messages eg, handover messages.

Both FACCH and SACCH operate in uplink and downlink directions.

Channel Planning


9

To calculate the CCCH requirements we first need to determine the number of CCCHblocks required to support PAGING AND ACCESS GRANT. From these two values wecan then calculate the number of CCCH blocks required for a particular cell.

Paging Blocks

Calculating CCCH blocks

Definition: the most important use of broadcast information is to set up channels for oneto one communication between the mobile transceiver and the base station. This is called paging.

Paging in GSM is carried out on a LAC basis. When mobile station (MS) is paged, a paging message is sent from the MSC to each BSC belonging to that MSC’s service area, or to those BSCs serving at least one cell belonging to the LA where the MS is registered. For each paging message received by the BSC, paging command messages have to be sent to all cells belonging to the LA where the target MS is registered.

Channel Planning


10

Paging Overview


11

• AGBLK The parameter AGBLK determines how many of the paging blocks per multi-frame that are reserved for the AGCH (Immediate Assignment).

• MFRMS This is the multi-frame period and defines the transmission interval of paging messages to the same paging group.

• Two types of channel configuration: - Combined BCCH/SDCCH : 3CCCH blocks - Non-combined BCCH/SDCCH: 9 CCCH blocks

The relation between MFRMS, AGBLK and the number of paging groups is: Combined BCCH/SDCCH cells: Number of paging groups = (3 - AGBLK) * MFRMS

Non combined BCCH/SDCCH cells: Number of paging groups = (9 - AGBLK) * MFRMS

Channel PlanningCalculating CCCH blocks


12

The number of paging group with different MFRMS and AGBLK setting

Channel Planning


13

Channel Planning


Non-combined BCCH/SDCCH

CCCH = 9AGBLK = 1

Then PGCH Block = 9 - 1 = 8

Assumption 1 PGCH Block = 1IMSI + 2TMSI = 8 * 3 = 24 Paging message

Paging message per second = 24/0.235 = 102 Paging message per secondPaging message per hours = 102 * 3600 = 367,660 paging message

Assumption 2 paging message per subscriber

Subscriber = 367,600/2 = 183,830

Erlangs = 183,830*0.025 = 4,600

Finally we can calculate number of TRXs per LAC


14

Normal paging load

Combined BCCH/SDCCH:

((AGBLK=0): 5060 Erlang = 1265 TRXs per LA (AGBLK=1): 3373 Erlang = 843 TRXs per LA

Non combined BCCH/SDCCH:

(AGBLK=0): 15180 Erlang = 3795 TRXs per LA (AGBLK=1): 13495 Erlang = 3373 TRXs per LA

By doing the estimation that each TRX roughly carry an average of 4 Erlang of traffic during busy hour,

Channel Planning



15

Channel Planning

High paging load

Combined BCCH/SDCCH:


Non combined BCCH/SDCCH:




16

There are a number of factors that will effect the SDCCH requirements in a GSM Cell as follows

-Call setup-SMS service-Location update

Calculating SDCCH

To determine the erlangs offered for SDCCH’s:

Time duration for location updates TLUTime duration for SMS (short message service set-up) TSMSTime duration for call set-up TcGuard time for SDCCH TgCall arrival rate per second call λcallLocation Update rate per second LU λ LUSMSs per hour SMS λsms

To determine the erlangs offered for SDCCH’s:

Erlangs offered =(λcall * [Tc] + λ LU * [TLU+Tg] + λsms * [TSMS+Tg])/3600

Channel Planning


17

Traffic in Erlang

An Erlang is a unit of telecommunications traffic measurement. Strictly speaking, an Erlang represents the continuous use of one voice path. In practice, it is used to describe the total traffic volume of one hour.

For example, if a group of user made 30 calls in one hour, and each call had an average call duration of 5 minutes, then the number of Erlangs this represents is worked out as follows.

Minutes of traffic in the hour = number of calls x durationMinutes of traffic in the hour = 30 x 5Minutes of traffic in the hour = 150Hours of traffic in the hour = 150 / 60Hours of traffic in the hour = 2.5 Erlang


18

Traffic Estimation

•Traffic varies between different hours, estimated traffic must be able to satisfy the peak loads. Busy hour traffic is typically twice that of the average. •Estimate number of subscribers

o Long-term predictiono Forecast Subscribers

• Expected traffic load per subscriber

• Particular habits of subscribers

• Busy hour conditionso Busy hour of the day o Traffic patterns


19

Calculating TCH timeslot channel

To determine the amount of carrier equipment required for a particular cell, the amount of traffic channels to be supported must be known. This can be determined by multiplying the subscriber density by the number of erlangs being given to one subscriber.

Sub density = 3,000 subsErlangs per sub = 0.025 ErlEstimated cell Erlang requirement = 3000*0.025 = 75 Erl

Number of timeslot required = 87 @ GOS 2% (Erlang B Table)

Number of TRX required = 11 TRXs

Channel Planning


20

CGI Planning

MCC: 3 digits (Mobile Country Code)As a global unique country identity standard, the MCC resources are allocated and managed by ITU in a unified manner.

MNC: 2 or 3 digits (Mobile Network Code)The MNC is usually allocated by the related telecom management authority of a country in a unified manner.

LAC: 1 to 65535 (Location Area Code), Start from 1010 to 1100 for Digicel

CI: 0 to 65535 (Cell Identity)For the allocation of the CI, there is no special restriction, and it can be any value within 0~65535 (decimal). However, you must ensure that not any two cells in one location area have the same CI.

Cell Global Identity = Mobile Country Code (MCC) + Mobile Network Code (MNC)+ Location Area Code + Cell Identity (CI)


21

Frequency Planning

GSM Frequency Spectrum

GSM900DL: 935-960 MHz UL:890-915 MHz200kHz Channel spacing --- > 124 ChannelsARFCN 1-124

E-GSMDL: 925-935 MHz UL:880-890 MHZ200 kHz Channel spacing --- > 50 ChannelsARFCN 0, 975-1023

GSM1800DL:1805-1880 MHz UL:1710-1785 MHz200 kHz Channel spacing --- > 374 ChannelsARFCN 512-885


22

Impact of Limited Frequency Spectrum

-Bandwidth is an expensive resource (limited)

-Best usage necessary

- Efficient planning necessary to contain good QoS when the Traffic in the network is increasing .

Frequency Planning


23

Frequency Planning


24


25

Frequency Planning

Advantages of Frequency Hopping

- Frequency diversity – reduces the affect of fading. At any location some frequencieswill be fading, some will not. This boosts the overall receive signal strength and the C/I ratio.

-Reduced overall interference – This lower overall average interference allows the error correction software to be more effective and reduces overall dropped calls and improves call quality.

-A reduction of overall interference and improvement in call quality allows a tighter frequency reuse to be used without degrading network quality. So sites can be upgraded to a higher capacity without increasing dropped calls and reducing call quality.


26

Reuse Cluster Size

- Sector sites- 4 sites per reuse cluster- 3 cells per site

- Reuse Cluster size:-4*3 = 12

Reuse Cluster Size

- Sector sites- 3 sites per reuse cluster- 3 cells per site

- Reuse Cluster size:- 3*3 = 3

Frequency Planning


27

Reuse Distance

D = f*R*√3*RCS

f = 1 , Omni-directional cells 2/3 , Three-Sector cellsR= Cell RadiusRCS= Number of cells per cluster

Frequency Planning


28

Baseband Hopping

The number of frequencies equals the number of TRX. The TRX do not retune but individual timeslots are switched to different TRX (with different frequencies) in a random or cyclical sequence.

It can be activated without the need for a retune. However, since the BCCH (and SDCCH) cannot hop it is better to plan a very clean BCCH frequency layer, and use a tighter reuse for TCH than BCCH.

Each TRX retunes to the new frequency every burst. The number frequencies used for hopping can be much more than the number of TRX in a cell. This gives better frequency diversity.

A new frequency plan is required because more frequencies are needed per cell than the number of TRXs. Again a good BCCH layer is required. However for TCH a number of groupings are possible

Synthesizer Hopping

Frequency Planning


29

• HSN: The Hopping Sequence Number specifies in which order the frequencies in the HFS shall be used for a CHGR when using frequency hopping. The sequence to be used can be either be a cyclic sequence or various pseudo-random sequences. To benefit from MAIO Management, cells within a site must have the same HSN. .

• MAIO: Mobile Allocation Index Offset Mobile Allocation Index Offset (MAIO) is a frequency offset set for all Basic Physical Channels (BPCs). Manual MAIO planning prevents adjacent channel interference within a cell as well as co- and adjacent channel interference in cosited cells when using frequency hopping.

Frequency Planning


30

Frequency Planning


31

Manual frequency planning

Mapbasic developed – the idea is to randomly check and evaluate frequency channel until the best one is found.

- MCOM- PIANO- XTracker- Lumpinee- MIPT...

Frequency Planning


32

Automatic frequency planning

The idea is to simulate frequencies and result the interference. The accuracy resultis depended on input data such as digital map, propagation model, drive testand etc.

AFP – ActrixILSA&Advantage – Aircom internationalTCPU - Ericsson....

Frequency Planning

Documents

Radio Parameter Planning