Second Annual Progress Seminar

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Second Annual Progress Seminar Supervisor Prof.
S. N. Merchant
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MPOE Prefiltering
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• ?DS-CDMA Limited by
• 1. MAI (Multiple users)
• 2. ISI (Multipath Channel)
• ? Multi-user signal processing overcomes MAI
  ISI
• ? Difficult to implement in handsets
• ? Ideally suitable for uplink transmission
• ? Prefiltering provides a way for downlink
  transmission

Signal MAI Noise
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System model for Joint Prefiltering
1. FIR filter 2. What is the criterion for design
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• ? MMSE optimal for AWGN channels.
• y x ?
  
• ? MPOE significantly better than MMSE in
  interference 1
• 
  y ?
• 
  
• ? We develop prefilter to minimize probability
  of error in
• mobile receiver
• ? FIR filter with complete channel knowledge

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• ? The chip waveform
• ? The signal for user u is
• 
  
• ? The total transmitted signal
• ? The x(t) is sampled and prefiltered

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• ? The received signal after matched filtering
• ? Conditional probability of error is
  formulated.
• 1. Since base station knows tx bits
• 2. Provides Linear complexity 1
• ? Conditional probability of error expression
  is
• 
  
• 
  

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• ? The joint conditional probability of error is
• ? By invoking independency assumption
• ? By invoking indentical assumption
• 
  
• 
  
• ? Simple gradient search is used to find the
  prefilter coefficients

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System model for Individual Prefiltering
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How to improve the performance further

• ?Diversity techniques can be used to improve
  performance.
• Instead of transmitting the signal through one
  antenna, we send it through M different antennae.
  
• ? Since the knowledge of the channel is assumed,
  we can
• take further advantage of this information

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• ? MRT provides full transmit antenna diversity
  when the channel information is available
• ? Channel estimation is not feasible at the
  receiver,
• hence STBC is not considered
• The beamforming weights are calculated adaptively
• ? MRT is suitable
• Does not require complex receiver
• Does not boost the transmit
  power

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The signal total signal
After simple manipulation
Signal transmitted from MRT m is
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• Simulation parameters
• Number of users 4 (U)
• Chip gain 128 (N)
• Correlation coefficients of PN code (0.1)
• Channel complex Gaussian mean 0.5 variance
  0.1655
• Channel FIR filter length 5
• Prefilter length 4

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MPOE Prefiltering for statistical channel
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Multihop cellular Network
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Cross layer routing protocol
Node constraints 1. Cooperation of the nodes.
2. Connectivity of the nodes. 3. The
interference caused by the call
initiating/forwarding nodes. Path
constraints 1. End-End throughput 2.
End-End delay
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Cooperations
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Connectivity

• We select nodes which has sufficient number of
  neighbors.
• We select nodes which has 5.1774(log(n))
  number of neighbors.
• To make sure that call is intact
• Reference
• F. Xue and P. Kumar, The number of neighbors
  needed for connectivity of wireless networks.
  SpringerWireless Networks, vol. 10, pp. 169.181,
  Mar 2004

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Interference
G -- Processing gain -- PN code cross
correlation n -- number of nodes Pij
-- Transmitted power
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End-End Throughput
? Defined as the probability of successful
transmission from source to destination
Which involves successful transmission
at each and every intermediate nodes.
The successful transmission from node i to node
its neighbor node j (single hop) occur
when the received SINR at node j
from node i is stronger than a ß
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? Message is successfully transmitted from source
1 to destination h is given by
?This gives lower bound on end-end throughput
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Simulation results
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Access Mechanism Design

• OFDM-CDMA based access mechanism
• Source node, destination node intermediate relay
  nodes will be grouped together
• CDMA PN code assigned to each group
• In a particular the hops are assigned with OFDM
  carriers

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Spreading codes are chosen according to the data
rate requirements
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Code reuse
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Open problems

• Capacity analysis
• At a time how many such a
  communication can take place for a given
  interference level
• Graph coloring problem
• 2. Code reuse
• Is it possible to reuse the CDMA
  spreading code at far distance
• 3. Proper NOVSF design
• Is it possible to reuse the CDMA
  spreading code at far distance

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Open problems

• Error propagation along the path
• 2. MPOE for multihop communication
• 3. Mobile to mobile fading channel design

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MIMO Relay networks
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Thanks