自适应调制介绍

7
Optimization based on SNR and Buffer Status
Performance Gain
8
Channel Status Indicator SNR • Divide SNR into several regions • Map each SNR region into a modulation and coding mode (usually higher SNR to higher data rate) • For each time interval, get a SNR value( For different system, there are different methods to calculate SNR) • Find the corresponding mode
Soft BER
Consecutive S/F
Historical S/F
Sample packet
19
Evaluation Works
SNR None Buffer Status ARQ HARQ Source Coding
Soft BER
Consecutive S/F
Historical S/F
Sample packet
20
Possible Opportunities • Theoretical works a) SNR estimation error characteristic and its relation to different AMC strategies in different channel b) Feedback error and feedback time influence c) Effect of correlated Rayleigh Fading with different Doppler frequencies d) Packet length effect
A sketch diagram
5
Optimization based on SNR and Buffer Status Denote the data traffic in the channel as T (γ )
Here
γ
is the SNR in the channel
The total packet loss probability is:
Optimization based on SNR and Buffer Status
The Process of the AMC 1. The transmitter transport the Buffer Status to the receiver 2. According to the Buffer Status, the receiver sets up a current SNR threshold for each data rate 3. According to the threshold and SNR, the receiver decide a Mode 4. The receiver transport the Mode to the transmitter 5. The transmitter will use the Mode to transmit the next frame
sk =| LLຫໍສະໝຸດ Baidu (k ) | P ( xk = 1 | r ) : yk = 1 log P ( xk = 0 | r ) = P ( xk = 0 | r ) log : yk = 0 P ( xk = 1 | r ) = log = log P ( xk = y k | r ) P ( xk ≠ y k | r ) 1 − pk pk
12
Channel Status Indicator
Sample Packet • Lower the bit rate if a number of consecutive failures occur • Every time interval( a certain number of packets), pick a random bit-rate from the set of bit-rates that may do better than the current one( no consecutive failures, higher throughput with in a window) • Send a packet using that bit rate instead of the current one • If this packet succeeds, use the new bit rate. Otherwise, keep the previous one.
Adaptive Modulation and Coding: a Cross-Layer View
05/23/2011
1
Adaptive Modulation & Coding System
Source Coding
Buffer
Transmitt er
Fading Channel
Receiver
P = b(T (γ )) + c(T (γ ), γ )
γ
if it is mapped into a higher bit rate
For a certain
T (γ )
Vice Versa
b(t (γ ))
c(t (γ ), γ )
6
Clearly, this is an optimization problem
9
Channel Status Indicator
Soft BER • Divide BER into several regions • Map each BER region into a modulation and coding mode (usually higher BER to lower data rate) • For each time interval, calculate a BER value in the receiver • Find the corresponding mode
21
Possible Opportunities • Evaluation works a) AMC with soft BER protocol in different channels b) Buffer status combined with all Channel Status Indicators • Others Channel status estimation • Different Criteria BER, Packet loss, Delay, Throughput, PSNR
11
Channel Status Indicator
Historical Success/ Failure Use a window of packets to calculate the number of packets with success or failure. • Increase the modulation rate if an opportunistic rate increase threshold is maintained • Decrease the modulation rate if a maximum tolerable loss threshold is exceeded
13
Channel Status Indicator
14
Channel Status Indicator
SNR Soft BER Consecutive Success/ Failure Historical Success/ Failure Sample Packet
Untrained SNR usually results in over-selection due to fast fading, multi-path etc. Trained SNR is much better than untrained SNR method 20% better than trained SNR
22
References
• Dinish Rajan,” Exploiting transmit buffer information at the receiver in block fading channels” • Joseph Camp, Edward Knightly, ”Modulation Rate Adaptation in Urban and Vehicular Environments: Cross-Layer Implementation and Experimental Evaluation” • Mythili Vutukuru, etc” Cross-Layer Wireless Bit Rate Adaptation” • Honghai Zhang, etc” Cross-layer optimization for streaming scalable video over fading wireless networks” • Anh Tuan Hoang, etc” Cross-layer Adaptive Transmission Optimal Strategies in Fading Channels” • Hong-Chuan Yang, etc” Analysis of Channel-Adaptive Packet Transmission Over Fading Channels With Transmit Buffer Management” • John C. Bicket, “bit-rate selection in wireless networks”
AMC ARQ
Adaptive Source Coding
2
Optimization based on SNR and Buffer Status
3
Optimization based on SNR and Buffer Status Objective BER of 10-4
4
Optimization based on SNR and Buffer Status
1 pk = sk 1+ e
10
Channel Status Indicator
Consecutive Success/ Failure • Increase the modulation rate after a number of consecutive successful transmissions • Decrease the modulation rate after a number of consecutive failures
15
Upper Layer Consideration
• Buffer Status
Source data rate distribution and channel capacity Buffer Size
• Delay Constrained
16
Upper Layer Consideration
Under-select in fast fading channels, sensitive to interference, inaccurate with in outdoor settings Under-select in fast fading channels, sensitive to interference, inaccurate with in outdoor settings in static environment with performance similar to Success/Failure protocol. Sensitive to coherence time
• ARQ (Automatic Repeat reQuest)
• HARQ(Hybrid Automatic Repeat reQuest)
17
Upper Layer Consideration
• Source Coding
18
Theoretical Works
SNR None Buffer Status ARQ HARQ Source Coding