Cooperative Communication Using Fountain Codes
We consider the transmission of information via a number of relay nodes. By using so-called rateless codes, we allow the receiver to accumulate information in a fast and energy-efficient way. During the past year, we have considered a number of theoretical as well as practical issues that are important for migration to products based on our technology. In particular, we have analyzed (i) the impact of nonorthogonality of the data streams transmitted by different nodes, (ii) the performance of the scheme in wireless channels with shadow fading, and (iii) analytical bounds on the performance of our previously suggested asynchronous transmission scheme.
Background & Objective: In cooperative communications with information accumulation, messages are transmitted from one node to another via several, parallel, relay nodes. At the receiver, the information from all the different relay nodes is added up. This is different from the conventional approach, where the energy from the different relay nodes is added up at the receiver. In order for the receiver to be able to distinguish the messages from different relay nodes, they have to be transmitted on orthogonal channels, e.g., using different spreading codes; nonorthogonality would result in inter-stream interference and thus lead to a reduction in performance.
Technical Discussion: As proposed in the previous year's phase of the project, the transmission from the source to the destination via several parallel relays uses rateless codes. They encode and transmit the source information in an infinitely long codestream; a receiver can recover the original information from unordered subsets of the codestream, once the total obtained mutual information from multiple sources marginally exceeds the entropy of the source information. During this year, we analyzed the impact of inter-stream interference, i.e., the case that the receiver cannot perfectly separate the information transmitted from different relay nodes on different CDMA spreading codes. We found that the impact of such interstream interference is very small; the reason being that the stream that contributes most to the total received mutual information is also the one that suffers least from the interstream interference. For our previously developed asynchronous transmission scheme, we developed an upper and lower bounds on the performance, which are related to the cases where the links between relay nodes are either extremely weak or extremely strong. Finally, we analytically derived the energy consumption and latency for our previously developed synchronous scheme in the case that the fading follows a lognormal distribution, which is relevant for the case that shadowing occurs in the channel.
Future Direction: Simulation of the scheme with realistic fountain codes, and implementation on a testbed.
Contacts:
Andreas F. Molisch
Jonathan Yedidia
Jinyun Zhang
Publications:
Draper, S.; Liu, L.; Molisch, A.; Yedidia, J. , "Iterative Linear-Programming-Based Route Optimization for Cooperative Networks", International Zurich Seminar on Communications (IZS), pp. 84-87, March 2008 (IZS 2008, TR2008-009)
Molisch, A.F.; Mehta, N.B.; Yedidia, J.S.; Zhang, J., "Performance of Fountain Codes in Collaborative Relay Networks", IEEE Transactions on Wireless Communications, ISSN: 1536-1276, Vol. 6, Issue 11, pp. 4108-4119, November 2007 (IEEE Explore, TR2007-082)
| Technical Reports: | |
| Cooperative Relay Networks Using Fountain Codes | |
Technology Area: Digital Communications
Modification Date: March 12, 2008
