Random Packet-CDMA: Reducing Delay and Increasing Throughput of WLAN Systems

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Random Packet-CDMA Reducing Delay and
IncreasingThroughput of WLAN Systems

• Roland Kempter and Behrouz Farhang-Boroujeny
• kempter_at_ece.utah.edu
• farhang_at_ece.utah.edu

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Organization

• Introduction Scheduled vs. Random Channel
  Access
• Random Packet-CDMA (RP-CDMA)
• RP-CDMA Header Detection
• RP-CDMA Payload Detection
• Conclusions

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Introduction scheduling-based access

• Advantages
• Base knows everything
• packet collisions can be avoided
• service can be guaranteed (great for voice)

• Disadvantages
• Resources need to be negotiated
• OK in circuit switched systems
• large overhead (or low efficiency) with
  packetized traffic

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Introduction random channel access

• Advantages
• self regulating (good for bursty traffic)
• load adaptive
• simplifies infrastructure

• Disadvantages
• Collisions, low stable throughput
• degrades heavily as load increases
• delay variations

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Introduction background on random channel access
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RP-CDMA packet structure KemAmiFar06,
SchKemKot06
KemAmiFar06 R. Kempter, P. Amini and B.
Farhang-Boroujeny, Throughput and Stability of
RP-CDMA and Spread Aloha in Multipacket Capture
Channels", submitted to IEEE/ACM Transactions on
Networking, October 2006 SchKemKot06 C.
Schlegel, R. Kempter and P. Kota, A Novel Random
Wireless Packet Multiple Access Method Using
CDMA, IEEE Trans. Wireless Communications, p.
1362-1370, Vol. 5, No. 6, June 2006
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RP-CDMA Performance interference in the header
channel
System Effect Packet format separates TX into a
virtual header and virtual data channel
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RP-CDMA Performance collisions in the header
channel
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RP-CDMA Header Detection results
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RP-CDMA header detection, spread aloha, equal
powers
(a) SNRh/SNRd5 dB
(b) NhNd20
(c) Ld / Lh25
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RP-CDMA performance

• Conclusions from the header process
• After a certain point which is f(N,SNR),
  increasing Ld / Lh
• does not improve performance

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RP-CDMA data channel performance
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RP-CDMA Data Detection

• Matched Filter TseHan99

• Decorrelator TseHan99

• MMSE TseHan99

• Partitioned Spreading KemSch05, ShiSchKem06
  iterative demodulation, resolves (virtually) all
  multiuser interference

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RP-CDMA network simulations

• IP packet sizes are trimodally distributed
  Inet2
• Pr(L50 bytes) 0.5
• Pr(L500 bytes) 0.4
• Pr(L1500 bytes) 0.1
• Also
• RP-CDMA header size Lh 50 bits ? ELd / Lh
  60
• Payload and header spreading gains N32
• Header/Payload SNR 5 dB
• Header and data detection thresholds 3 dB
• Power control
• Nodes transmit to a central base station

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RP-CDMA equal power, central base station
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RP-CDMA receiver SOFTWARE DEFINED RADIO
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Conclusions 1/2

• We demonstrated the performance in the RP-CDMA
• header channel by modeling it as a Spread Aloha
  packet.

• After a point, RP-CDMA becomes interference
  rather than collision limited
• f (Nh, Nd, K, Ph/Pd, pathloss, ?, h.
  technology, d. technology)

• For the data channel, we compared
• - Matched Filter - Decorrelator - MMSE
• - Partitioned Spreading
• in base station centric networks w/ power control

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Conclusions 2/2

• RP-CDMA is determined by header process
• improving header directly is hard (non-linear in
  parameters)
• BUT with Partitioned Spreading, for a
  targeted data rate, Pd can be low, increasing
  Ph / Pd
• ? pushing the interference limit

• We presented the general block-diagram of an
  RP-CDMA
• software defined receiver

• RP-CDMA allows to adopt to different load
  situations via software changes
• low load power save w/ matched filter
• high load partitioned spreading

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The End
Additional References