A Medium Access Protocol for Interconnecting ATM and Wireless Networks

• Time division multiple access/frequency division duplex.

• Voice mobiles require real-time service. NC-PRMA scheme.

• Available bit rate services are provided for (delay insensitive) data mobiles. DQRUMA scheme.

• Talkspurt only mobiles can allocate information slots.

• Hybrid protocol is compared with PRMA and Reservation TDMA.

• Real time mobiles are assigned their own control slots in the uplink.

• Delay insensitive mobiles are required to transmit their requests for information slots in contention with others through the random access slots in the uplink.

Issues• Distributed mobile-executed handoff scheme:

-Cell size ~order of 100m #handoffs >> #handoffs in traditional cellular networks.-Each mobile is assigned several VCI when it is admitted to the system.-A VCI is sent along with the mobile packet.

• Size of the Data Packets 106 bytes for each user data packet.• Use of Control Slots?

Guarantee that the access delay experienced by the real-time mobiles is limited to approximately one frame period. Stabilize the system under heavy traffic load.Silent mobile’s control slot can be used to transmit system related information to the base station without any contention.

Voice Control SlotsData Random Access Slots Information Slots

Uplink TDMA frame

VoicePollingSlots

Information SlotsStatusSlot

DataAttention

Slots

VoiceAttention

Slots

DataPollingSlots

Downlink TDMA frame

Structure of the TDMA frame

Organization of the TDMA frames

• Status SlotInforms the mobiles about the number of voice control slots in the uplink and which of them are idle. Used in Handoff.Can be used to indicate the level of activities in the data random access slots that the data mobile can adapt to different situations dynamically.(e.g. changing transmision probability)

• Polling Slots/Attention SlotsBase station notifies mobiles with new requests, they succeeded, through polling slots.Attention slots instruct mobiles to tune to downlink information slots for packets.

Hand-shakings Description

• Sending Packets from Voice Mobile.1.Talkspurt begins.2.Mobile uses its control slot to send a request for an uplink information slot.3.Mobile’s ID and location of information slot allocated are passed to the mobile through the polling slots.4.Mobile listens to the polling slots acknowledges through the voice control slot, transmits its packets using the assigned information slots and reserves or releases its information slot by piggybacking.

• Sending Packets from Data Mobile.1.Mobile sends request through random access slots mobile’s ID is included.2.Base acknowledges through polling slots and if there is no collision informs the mobile which uplink information slot to use.

• Sending Voice/Data Packets from Base.1.Base informs mobiles to listen to downlink information slots through attention slots.2.Mobile’s ID, number and location of information slots, is transmited, packets are sent in the assigned information slots.3.Mobile acknowledges through the control slot/random access slots and starts listening to the packets in the assigned downlink information slots.

Comparison to others/Design issues• Voice control slots in the downlink have been replaced by

polling and attention slots.Delay requirements are met because of the base station’s complete control over the downlink.

• The hybrid structure is believed to be able to support the two different classes of mobiles simultaneously.The number of control slots and random access slots can be changed depending on the number of different types of mobiles in the system.

• Significant amount of bit rate can be saved by using polling and attention slots rather than control slots in the downlink because only a fraction of silent voice mobiles will make a transition. Thus more of these can be sent if traffic is heavier in the downlink. The base station can poll the data mobiles periodically to alleviate the contention.

Frame period 12.5 msSize of an Information slot 900 (=848(=2*53*8)+52) bits Num. Of info, slots per frame 10Size of an overhead slot 60 bitsNum. Of overhead slots per frame 15Channel Rate 792 kbpsAvg. voice talkspurt duration 1 sAvg voice silence duration 1.35 s Buffer size of voice mobiles 1 packetBuffer size of data mobiles 10 packets

Protocol Uplink DownlinkHybrid 8 voice control slots

7random access data control slots14 attention/polling1 status slot

RTDMA 15 Random access slotsPRMA system 1 90 bits /packetPRMA system 2 11 frames instead of 10

Overhead

Data model 1 talkspurt/silence average duration 1/1.35Data model 2 talkspurt/silence average duration 0.33/1.35

Simulation Parameters

Figure 2: Voice Dropping probability (System 1 and Data Model 1)

0,001

0,01

0,1

5 5,5 6 6,5 7 7,5 8 8,5 9 9,5 10Number of data users

Voic

e D

ropp

ing

Pro

babi

lity

Hybrid

PRMA 0,5, 0,5

PRMA 0,5, 0,7

PRMA 0,7, 0,7

RTDMA

8 Voice users (Data Model 1)

Figure 3: Data Dropping probability (System 1 and Data Model 1)

0,00001

0,0001

0,001

0,01

0,1

5 5,5 6 6,5 7 7,5 8 8,5 9 9,5 10

Number of data users

Dat

a D

rop

pin

g P

rob

abil

ity

Hybrid

PRMA 0,5, 0,5

PRMA 0,5, 0,7

PRMA 0,7, 0,7

RTDMA

8 Voice users (Data Model 1)

Figure 4: Voice Dropping Probability (System 1 and Data Model 2)

0,001

0,01

0,1

6 8 10 12 14 16 18Number of data users

Vo

ice

Dro

pp

ing

Pro

bab

ility

Hybrid

PRMA 0,3, 0,7

PRMA 0,5, 0,7

PRMA 0,7, 0,7

RTDMA

8 Voice users (Data Model 2)

Figure 5: Data Dropping Probability (System 1 and Data Model 2)

0,00001

0,0001

0,001

0,01

0,1

6 8 10 12 14 16 18Number of data users

Dat

a D

rop

pin

g P

rob

abil

ity

Hybrid

PRMA 0,3, 0,7

PRMA 0,5, 0,7

PRMA 0,7, 0,7

RTDMA

8 Voice users (Data Model 2)

If Pdd=0,001 and Pvd=0,01 12 mobiles can be supported using hybrid and RTDMAwhile 10 using PRMA

Figure 6: Voice Access Delay (System 1 and Data Model 1)

0,5

1

1,5

2

2,5

3

5 5,5 6 6,5 7 7,5 8 8,5 9 9,5 10

Number of data users

Vo

ice

Acc

ess

Del

ay (

fram

es)

Hybrid

PRMA 0,5, 0,5

PRMA 0,5, 0,7

PRMA 0,7, 0,7

RTDMA

8 Voice users (Data Model 1)

Figure 7: Data Access Delay (System 1 and Data Model 1)

0

0,5

1

1,5

2

2,5

3

5 5,5 6 6,5 7 7,5 8 8,5 9 9,5 10

Number of data users

Dat

a A

cces

s D

elay

(fr

ames

)

Hybrid

PRMA 0,5, 0,5

PRMA 0,5, 0,7

PRMA 0,7, 0,7

RTDMA

8 Voice users (Data Model 1)

Figure 8: Voice Dropping Probability (System 2 and Data Model 2)

0,001

0,01

6 8 10 12 14 16 18

Number of data users

Vo

ice

Dro

pp

ing

Pro

bab

ility

Hybrid

PRMA 0,3, 0,7

PRMA 0,5, 0,7

PRMA 0,7, 0,7

RTDMA

8 Voice users (Data Model 2, System 2)

If Pdd=0,001 and Pvd=0,01 13 mobiles can be supported for RPMA (12 for Hybrid & RTDMA)

Figure 9: Data Dropping Probability (System 2 and Data Model 2)

0,00001

0,0001

0,001

0,01

6 8 10 12 14 16 18

Number of data users

Dat

a D

rop

pin

g P

rob

abili

ty

Hybrid

PRMA 0,3, 0,7

PRMA 0,5, 0,7

PRMA 0,7, 0,7

RTDMA

8 Voice users (Data Model 2, System2)

Conclusions

• For average access delays PRMA gives the best performance

• The performance is similar to RTDMA while there are advantages:1. Optimal Transmission probability for data mobiles can be easily determined be trial and error, given the number of voice mobiles.2. Separating the contention of data mobiles from the voice mobiles makes the hybrid protocol more stable and allows the quality of service.