Ashish Kumar MeshramRoll No. mt1402102002M.Tech. Communication & Signal ProcessingDiscipline of Electrical Engineering
IIT – Indore | EE642 | Wireless Communication
COOPERATIVEDIVERSITY
An Introduction to Cooperative Communication
01IIT – Indore | EE642 | Wireless Communication
Contents
Motivation
Introduction
Application Scenario
Relay Channel
Cooperation Protocols
Pros and Cons of cooperation
System Tradeoffs
References
Multiple transmit antennas provide spatial diversity
Unfortunately, this is not easy to implement in the uplink of a cellular system, due to the size of the mobile unit
How to overcome this limitation?
In order to overcome this limitation, yet still emulate transmit antenna diversity, an alternative form of spatial diversity is being considered, where diversity gains are achieved via the cooperation of in-cell users.
02IIT – Indore | EE642 | Wireless Communication
Motivation
Tx Rx
Introduction
Sendonaris, A., Erkip, E., Aazhang, B.: User cooperation diversity–Part I: System description” and “User cooperation diversity–Part II: implementation aspects and performance analysis. IEEE Transactions on
Communications 51(11) 1927–1938 and 1939–1948 (2003)
Andrew Sendonaris, User Cooperation Diversity—Part I - System Description03IIT – Indore | EE642 | Wireless Communication
Motivation
– In each cell, each user may have a ‘partner.’
– Each of the two partners would be responsible for transmitting not only their own information, but also the information of their partner, which they receive and detect.
– Spatial diversity would be achieved through the use of the partner’s antenna.
𝑌0 𝑡 = ℎ10𝑋1 𝑡 + ℎ20𝑋2 𝑡 + 𝑛0(𝑡)
𝑌1 𝑡 = ℎ21𝑋2 𝑡 + 𝑛1(𝑡)
𝑌2 𝑡 = ℎ12𝑋1 𝑡 + 𝑛2(𝑡)
The mathematical formulation of the model is:
System Modeling and Channel Model
Andrew Sendonaris, User Cooperation Diversity—Part I - System Description04IIT – Indore | EE642 | Wireless Communication
Motivation Probability of outage
𝑇𝑥1
𝑇𝑥2
𝑅𝑥𝑐ℎ𝑎𝑛𝑛𝑒𝑙
05IIT – Indore | EE642 | Wireless Communication
Cooperative DiversityIntroduction
Cooperative diversity is a cooperative multiple antenna technique for improving or maximizing total network channel capacities for any given set of bandwidths which exploits user diversity by decoding the combined signal of
the relayed signal and the direct signal in wireless multihop networks.[
[
– A conventional single hop system uses direct transmission where a receiver decodes the information only based on
the direct signal while regarding the relayed signal as interference, whereas the cooperative diversity considers the
other signal as contribution;
– Cooperative diversity makes use of available mobile terminals as relays that cooperate together to form a virtual
antenna array
– The relay channel can be thought of as an auxiliary channel to the direct channel between the source and
destination;
– A key aspect of the cooperative communication process is the processing of the signal received from the source node
done by the relay;
– These different processing schemes result in different cooperative communications protocol
Cooperative Communications and Networking, K. J. Ray Liu, Ahmed K. Sadek, Weifeng Su, Andres Kwasinski 06IIT – Indore | EE642 | Wireless Communication
Cooperative DiversityIntroduction
– Cellular Capacity and Coverage Extension
– WLAN Capacity and Coverage Extension
– Vehicle-to-Vehicle Communication
– Wireless Sensor Networks
Cooperative Communications Hardware Channel and PHY, Mischa Dohler Yonghui Li
a b
c d
07IIT – Indore | EE642 | Wireless Communication
Application Scenario
Source Destination
Relay
𝑝(𝑦1, 𝑦2|𝑥, 𝑥12)𝑋
𝑋12 𝑌1𝑌2
08IIT – Indore | EE642 | Wireless Communication
IntroductionRelay Channel
– In information theory, a relay channel is a probability model of the communication between a sender and a receiver aided by one or more intermediate relay nodes;
– The RC is a three-terminal channel composed of a source node, a destination node, and one node called the relay, which is neither a source nor a sink;
– The role of the relaying node is to improve the overall performance of the communication between the source and destination.
Mathematically speaking, the RC consists of four finite sets:𝑋, 𝑋12, 𝑌1,and 𝑌1
and a collection of probability distributions:𝑝(𝑦1, 𝑦2|𝑥, 𝑥12)
ℎ𝑠,𝑑
ℎ𝑠,𝑟 ℎ𝑟,𝑑
𝑆𝑜𝑢𝑟𝑐𝑒 𝐷𝑒𝑠𝑡𝑖𝑛𝑎𝑡𝑖𝑜𝑛
𝑅𝑒𝑙𝑎𝑦
𝑃1
𝑃2
Phase 1Phase 2
09IIT – Indore | EE642 | Wireless Communication
Simplified Cooperation Model - Single Relay System ModelRelay Channel
Phase 1: From SourceTransmitted signal received by relay;
𝑦𝑠,𝑟 = 𝑃ℎ𝑠,𝑟𝑥 + 𝑛𝑠,𝑟Transmitted signal received by destination;
𝑦𝑠,𝑑 = 𝑃ℎ𝑠,𝑑𝑥 + 𝑛𝑠,𝑑Phase 2: From RelayTransmitted signal received by destination;
𝑦𝑟,𝑑 = ℎ𝑟,𝑑𝑞(𝑦𝑠,𝑟) + 𝑛𝑟,𝑑
…(1)
… (2)
… (3)
Cooperative Communications and Networking, K. J. Ray Liu, Ahmed K. Sadek, Weifeng Su, Andres Kwasinski
10IIT – Indore | EE642 | Wireless Communication
Simplified Cooperation Model - Single Relay System ModelRelay Channel
Cooperative Communications and Networking, K. J. Ray Liu, Ahmed K. Sadek, Weifeng Su, Andres Kwasinski
ℎ𝑠,𝑑; channel coefficients from source to destination
𝑥; transmitted information symbol
𝑃 ; transmitted power
𝑛𝑠,𝑑; additive noise for source to destination
𝑞(∙); function depending on processing implemented at relay
𝛿𝑠,𝑑2 ; variance of source to destination
𝛿𝑠,𝑟2 ; variance of source to relay
𝑛𝑠,𝑟; additive noise for source to relay
ℎ𝑠,𝑟; channel coefficients from source to relay
ℎ𝑟,𝑑; channel coefficients from relay to destination
𝑛𝑟,𝑑; additive noise for relay to destination
𝛿𝑟,𝑑2 ; variance of relay to destination
11IIT – Indore | EE642 | Wireless Communication
Relay Channel
– Fixed Cooperation Strategies
– Adaptive Cooperation Strategies
In fixed relaying, the channel resources are divided between the source and the relay in a fixed (deterministic) manner. The processing at the relay differs according to the employed protocols.
– AF (Amplify-and-Forward) Protocol– DF (Decode-and-Forward) Protocol– CF (Compress-and-forward) Protocol
– Selective DF– Incremental
Fixed relaying suffers from deterministic loss in the transmission rate. Moreover, fixed DF relaying suffers from the fact that the performance is limited by the weakest source–relay and relay–destination channels which reduces the diversity gains to one. To overcome this problem, adaptive relaying protocols can be developed to improve the inefficiency.
Cooperation Protocols
𝛽𝑟 =𝑃
𝑃 ℎ𝑠,𝑟2+ 𝑁0
𝑆𝑁𝑅𝑠,𝑑 = Γ ℎ𝑠,𝑑2
The relay does that by simply scaling the received signal by a factor that is inversely proportional to the received power, which is denoted by
…(6)
The SNR from the source link is given by
where Γ = 𝑃 𝑁0
…(7)
12IIT – Indore | EE642 | Wireless Communication
Amplify-and-ForwardCooperation Protocols
Cooperative Communications and Networking, K. J. Ray Liu, Ahmed K. Sadek, Weifeng Su, Andres Kwasinski
Transmitted signal received by relay;
𝑦𝑠,𝑟 = 𝑃ℎ𝑠,𝑟𝑥 + 𝑛𝑠,𝑟Transmitted signal received by destination;
𝑦𝑠,𝑑 = 𝑃ℎ𝑠,𝑑𝑥 + 𝑛𝑠,𝑑
…(4)
… (5)
In a fixed AF relaying protocol, which is often simply called an AF protocol, the relay scales the received version and transmits an amplified version of it to the destination.[
[
In Phase 1:
𝑦𝑟,𝑑 =𝑃
𝑃 ℎ𝑠,𝑟2+ 𝑁0
ℎ𝑟,𝑑𝑦𝑠,𝑟 + 𝑛𝑟,𝑑
𝑦𝑟,𝑑 =𝑃
𝑃 ℎ𝑠,𝑟2+ 𝑁0
𝑃ℎ𝑟,𝑑ℎ𝑠,𝑟𝑥 + 𝑛𝑟,𝑑′
𝑁0′ =
𝑃 ℎ𝑟,𝑑2
𝑃 ℎ𝑠,𝑟2+ 𝑁0
+ 1 𝑁0
The received signal at the destination in phase 2 according to eq. (6) is given by
…(8)
… (9)
where 𝑛𝑟,𝑑′ =
𝑃
𝑃 ℎ𝑠,𝑟2+𝑁0
ℎ𝑟,𝑑𝑛𝑠,𝑟 + 𝑛𝑟,𝑑
13IIT – Indore | EE642 | Wireless Communication
Amplify-and-ForwardCooperation Protocols
Cooperative Communications and Networking, K. J. Ray Liu, Ahmed K. Sadek, Weifeng Su, Andres Kwasinski
In Phase 2:
From eq. (4);
Assuming that the noise terms 𝑛𝑟,𝑑and 𝑛𝑠,𝑟 are independent
…(10)
𝑦 = 𝑎1𝑦𝑠,𝑑 + 𝑎2𝑦𝑟,𝑑
𝑎1 =𝑃ℎ𝑠,𝑑
∗
𝑁0
𝑎2 =
𝑃
𝑃 ℎ𝑠,𝑟2+ 𝑁0
𝑃ℎ𝑠,𝑟∗ ℎ𝑟,𝑑
∗
𝑃 ℎ𝑟,𝑑2
𝑃 ℎ𝑠,𝑟2+ 𝑁0
+ 1 𝑁0
𝛾 = 𝛾1 + 𝛾2
14IIT – Indore | EE642 | Wireless Communication
Amplify-and-ForwardCooperation Protocols
Cooperative Communications and Networking, K. J. Ray Liu, Ahmed K. Sadek, Weifeng Su, Andres Kwasinski
The destination receives two copies from the signal x through the source link and relay link. With knowledge of the
channel coefficients the output of the MRC detector at the destination can be written as
The combining factors 𝑎1 and 𝑎2 should be designed to maximize the combined SNR. Therefore, 𝑎1 and 𝑎2 are given by
…(11)
… (12)
By assuming that the transmitted symbol x in eq. (3) has average energy 1, the instantaneous SNR of the MRC output is
…(13)
𝛾2 =
𝑎1𝑃
𝑃 ℎ𝑠,𝑟2+ 𝑁0
𝑃ℎ𝑟,𝑑ℎ𝑠,𝑟
2
𝑁0′ 𝑎2
2 =
𝑃2
𝑃 ℎ𝑠,𝑟2+ 𝑁0
ℎ𝑠,𝑟2ℎ𝑟,𝑑
2
𝑃 ℎ𝑟,𝑑2
𝑃 ℎ𝑠,𝑟2+𝑁0
+ 1 𝑁0
=1
𝑁0
𝑃2 ℎ𝑠,𝑟2ℎ𝑟,𝑑
2
𝑃 ℎ𝑠,𝑟2+ 𝑃 ℎ𝑟,𝑑
2+ 𝑁0
From the above, the instantaneous mutual information as a function of the fading coefficients for amplify-and-forward is given by
𝐼𝐴𝐹 =1
2log 1 + 𝛾1 + 𝛾2 =
1
2log(1 + Γ ℎ𝑠,𝑑
2+ 𝑓(Γ ℎ𝑠,𝑟
2, Γ ℎ𝑟,𝑑
2))
where 𝑓 𝑥, 𝑦 ≜𝑥𝑦
𝑥+𝑦+1
𝛾1 =𝑎1 𝑃ℎ𝑠,𝑑
2
𝑎12𝑁0
=𝑃 ℎ𝑠,𝑑
2
𝑁0
15IIT – Indore | EE642 | Wireless Communication
Amplify-and-ForwardCooperation Protocols
Cooperative Communications and Networking, K. J. Ray Liu, Ahmed K. Sadek, Weifeng Su, Andres Kwasinski
where
…(14)
…(15)
…(16)
…(17)
The outage probability can be obtained by averaging over the exponential channel gain distribution, as follows:
Pr 𝐼𝐴𝐹 < 𝑅 = Εℎ𝑠,𝑑,ℎ𝑠,𝑟,ℎ𝑟,𝑑1
2log(1 + Γ ℎ𝑠,𝑑
2+ 𝑓(Γ ℎ𝑠,𝑟
2, Γ ℎ𝑟,𝑑
2)) < 𝑅
Calculating the above integration, the outage probability at high SNR is given by
Pr 𝐼𝐴𝐹 < 𝑅 ≃𝜎𝑠,𝑟2 +𝜎𝑟,𝑑
2
2𝜎𝑠,𝑟2 (𝜎𝑠,𝑟
2 𝜎𝑠,𝑟2 )
22𝑅 − 1
Γ
2
where the multiplicative factor of 2 in 2R is because half of the bandwidth is lost in cooperation by allocating them to the relay. The outage expression decays as −2, which means that the AF protocol achieves diversity 2.
16IIT – Indore | EE642 | Wireless Communication
Amplify-and-ForwardCooperation Protocols
Cooperative Communications and Networking, K. J. Ray Liu, Ahmed K. Sadek, Weifeng Su, Andres Kwasinski
…(18)
… (19)
17IIT – Indore | EE642 | Wireless Communication
Decode-and-ForwardCooperation Protocols
Cooperative Communications and Networking, K. J. Ray Liu, Ahmed K. Sadek, Weifeng Su, Andres Kwasinski
In a fixed DF relaying protocol, the relay decodes the received signal, re-encode it and then transmit to the destination.[
[
𝐼𝐷𝐹 =1
2min log 1 + Γ ℎ𝑠,𝑟
2, log(1 + Γ ℎ𝑠,𝑑
2+ Γ ℎ𝑟,𝑑
2)
where the min operator in the above equation takes into account the fact that the relay only transmits if decoded correctly, and hence the performance is limited by the weakest link between the source–destination and source–relay.
The outage probability for the fixed DF relaying scheme is given by Pr 𝐼𝐷𝐹 < 𝑅 ; Since log is a monotonic function, the outage event is equivalent to
min ℎ𝑠,𝑟2, ℎ𝑠,𝑑
2+ ℎ𝑟,𝑑
2<22𝑅 − 1
Γ
… (20)
… (21)
The mutual information for decode-and-forward transmission in terms of the channel fades can be given by
18IIT – Indore | EE642 | Wireless Communication
Decode-and-ForwardCooperation Protocols
Cooperative Communications and Networking, K. J. Ray Liu, Ahmed K. Sadek, Weifeng Su, Andres Kwasinski
The outage probability can be written as
Pr 𝐼𝐷𝐹 < 𝑅 = Pr ℎ𝑠,𝑟2<22𝑅 − 1
Γ+ Pr ℎ𝑠,𝑟
2>22𝑅 − 1
ΓPr ℎ𝑠,𝑑
2+ ℎ𝑟,𝑑
2<22𝑅 − 1
Γ
Since the channel is Rayleigh fading, the above random variables are all exponential random variables with parameter one. Averaging over the channel conditions, the outage probability for decode-and-forward at high SNR is given by
Pr 𝐼𝐷𝐹 < 𝑅 ≃1
𝜎𝑠,𝑟2
22𝑅 − 1
Γ
… (22)
… (23)
19IIT – Indore | EE642 | Wireless Communication
Compress-and-forward cooperationCooperation Protocols
Cooperative Communications and Networking, K. J. Ray Liu, Ahmed K. Sadek, Weifeng Su, Andres Kwasinski
The main difference between compress-and-forward and decode/amplify-and-forward is that while in the later the relay transmits a copy of the received message, in compress-and-forward the relay transmits a quantized and compressed version of the received message. Therefore, the destination node will perform the reception functions by combining the received message from the source node and its quantized and compressed version from the relay node
20IIT – Indore | EE642 | Wireless Communication
Selective DFCooperation Protocols
Cooperative Communications and Networking, K. J. Ray Liu, Ahmed K. Sadek, Weifeng Su, Andres Kwasinski
In a selective DF relaying scheme, if the signal-to-noise ratio of a signal received at the relay exceeds a certain threshold, the relay decodes the received signal and forwards the decoded information to the destination. On the other hand, if the channel between the source and the relay suffers a severe fading such that the signal-to-noise
ratio falls below the threshold, the relay idles.[
[
𝐼𝑆𝐷𝐹 =
1
2log 1 + 2Γ ℎ𝑠,𝑑
2,
1
2log 1 + Γ ℎ𝑠,𝑑
2+ Γ ℎ𝑟,𝑑
2,
1
2log 1 + 2Γ ℎ𝑠,𝑑
2,
1
2log 1 + Γ ℎ𝑠,𝑑
2+ Γ ℎ𝑟,𝑑
2,
ℎ𝑠,𝑟2< 𝑔(Γ)
ℎ𝑠,𝑟2≥ 𝑔(Γ)
where 𝑔 Γ =22𝑅−1
Γ
…(24)
… (25)
The mutual information for selective DF relaying is given by
21IIT – Indore | EE642 | Wireless CommunicationCooperative Communications and Networking, K. J. Ray Liu, Ahmed K. Sadek, Weifeng Su, Andres Kwasinski
The outage probability for selective relaying can be derived as follows. Using the law of total probability, conditioning on whether the relay forwards the source signal or not, we have
𝑃𝑟 𝐼𝑆𝐷𝐹 < 𝑅 = 𝑃𝑟 𝐼𝑆𝐷𝐹 < 𝑅| ℎ𝑠,𝑟2< 𝑔(Γ) Pr ℎ𝑠,𝑟
2< 𝑔(Γ)
+𝑃𝑟 𝐼𝑆𝐷𝐹 < 𝑅| ℎ𝑠,𝑟2> 𝑔(Γ) Pr ℎ𝑠,𝑟
2> 𝑔(Γ)
From eq.(24), the outage probability for selective DF relaying is given by
𝑃𝑟 𝐼𝑆𝐷𝐹 < 𝑅 = 𝑃𝑟1
2log 1 + 2Γ ℎ𝑠,𝑑
2< 𝑅| ℎ𝑠,𝑟
2< 𝑔(Γ) Pr ℎ𝑠,𝑟
2< 𝑔(Γ)
+𝑃𝑟1
2log 1 + Γ ℎ𝑠,𝑑
2+ Γ ℎ𝑟,𝑑
2< 𝑅| ℎ𝑠,𝑟
2> 𝑔(Γ) Pr ℎ𝑠,𝑟
2> 𝑔(Γ)
… (26)
… (27)
Cooperation Protocols Selective DF
22IIT – Indore | EE642 | Wireless CommunicationCooperative Communications and Networking, K. J. Ray Liu, Ahmed K. Sadek, Weifeng Su, Andres Kwasinski
Cooperation Protocols Selective DF
Calculating the above integration, the outage probability at high SNR is given by
Pr 𝐼𝑆𝐷𝐹 < 𝑅 ≃𝜎𝑠,𝑟2 +𝜎𝑟,𝑑
2
2𝜎𝑠,𝑟2 (𝜎𝑠,𝑟
2 𝜎𝑠,𝑟2 )
22𝑅 − 1
Γ
2
…(28)
which has the same diversity gain as the AF case. This means that at high SNR, both selective DF relaying and AF relaying have the same diversity gain.
23IIT – Indore | EE642 | Wireless CommunicationCooperative Communications and Networking, K. J. Ray Liu, Ahmed K. Sadek, Weifeng Su, Andres Kwasinski
Cooperation Protocols Incremental Relaying
For incremental relaying, it is assumed that there is a feedback channel from the destination to the relay. The destination sends an acknowledgement to the relay if it was able to receive the source’s message
correctly in the first transmission phase, so the relay does not need to transmit.[
[
Laneman, J.N., Tse, D.N.C., Wornell, G.W.: Cooperative diversity in wireless networks: Efficient protocols and outage behavior. IEEE Transactions on Information Theory 50(12), 3062–3080 (2004)
References
24IIT – Indore | EE642 | Wireless Communication
Outage Probabilities versus 𝑺𝑵𝑹𝒏𝒐𝒓𝒎
– Performance Gains– Balanced Quality of Service– Infrastructure-Less Deployment– Reduced Costs
– Complex Schedulers– Increased Overhead– Partner Choice– Increased Interference– Extra Relay Traffic– Increased End-to-End Latency– Tight Synchronization– More Channel Estimates
25IIT – Indore | EE642 | Wireless Communication
Pros & Cons
– Coverage versus Capacity
– Algorithmic versus Hardware Complexity
– Interference versus Performance
– Ease-of-Deployment versus Performance
– Cost versus Performance
Ease-of-Deployment
Interference Performance Cost
Coverage ↔ Capacity Algorithmic ↔ Hardware
Cooperative Communications Hardware Channel and PHY, Mischa Dohler Yonghui Li26IIT – Indore | EE642 | Wireless Communication
System Tradeoffs
At a given performance level, coverage can be traded capacity and algorithmic with hardware complexity. Performance can also be traded against amount of interference, ease-of-deployment and cost[
[
27IIT – Indore | EE642 | Wireless Communication
References
Bibliography:
Literatures:
1. Sendonaris, A., Erkip, E., Aazhang, B.: User cooperation diversity–Part I: System description” and “User cooperation diversity–Part II: implementation aspects and performance analysis. IEEE Transactions on Communications 51(11) 1927–1938 and 1939–1948 (2003)
2. Laneman, J.N., Wornell, G.W.: Distributed space-time-coded protocols for exploiting cooperative diversity in wireless networks. IEEE Transactions on Information Theory 49(10), 2415–2425 (2003)
3. Scaglione, A., Hong, Y.-W.: Opportunistic large arrays: Cooperative transmission in wireless multihop ad hoc networks to reach far distances. IEEE Transactions on Signal Processing 51(8), 2082–2092 (2003)
4. Laneman, J.N., Tse, D.N.C., Wornell, G.W.: Cooperative diversity in wireless networks: Efficient protocols and outage behavior. IEEE Transactions on Information Theory 50(12), 3062–3080 (2004)
1. K. J. Ray Liu, Ahmed K. Sadek, Weifeng Su, Andres Kwasinski: Cooperative Communications and Networking2. Mischa Dohler Yonghui Li: Cooperative Communications Hardware Channel and PHY3. Savo G Glisic: Advanced Wireless Communications, 2e
THANKSAshish Meshram