Low complexity delay-tolerant space-time block coding

Lead Research Organisation: University of Reading
Department Name: Sch of Systems Engineering

Abstract

Future wireless systems are expected to involve a plethora of small, low-cost communication nodes which will be widely distributed in the infrastructure of cities to provide truly pervasive and seamless communication and other services such as sensor networks. Perhaps the most fundamental challenge in these systems as in all wireless communications is channel fading. In these pervasive wireless systems, however, the individual nodes may be equipped with only a single antenna due to cost and size constraints. One powerful strategy to combat channel fading in the above systems is to apply space-time block coding (STBC) in a distributed fashion: creating and harnessing space diversity by enabling a cluster of wireless nodes to relay signals for each other and effectively create a distributed (or virtual) antenna array - with each relay node serving as one antenna element in the STBC array. A major challenge to distributed STBC is that the system is fundamentally asynchronous: signals from the relay nodes tend to arrive at the destination node at different times. Most existing works so far have focused on recerver based schemes. To tackle the above challenge more effectively, this proposal will employ a more fundamental and flexible approach: developing coding and modulation structures which are inherently delay-tolerant (coherent or non-coherent). In this way we move at least part of the problem from the receiver to the transmitter. Considering the fact that most wireless nodes are powered by batteries, equally important is to ensure low complexity both at the relays and at the receiver. The results of this project will enable the so far largely theoretical benefits of cooperative diversity to be realised in practical wireless networks.
 
Description - In cooperative communication networks, owing to the nodes' arbitrary geographical locations and individual oscillators, the system is fundamentally asynchronous. This damages some of the key properties of the space-time codes and can lead to substantial performance degradation. We studied the design of linear dispersion codes (LDCs) for such asynchronous cooperative communication networks, and achieved the following results:
(1) the concept of conventional LDCs was extended to the delay-tolerant version and new design criteria are established;
(2) a new design method was proposed to yield delay-tolerant LDCs that reach the optimal Jensen's upper bound on ergodic capacity as well as minimum average pairwise error probability. The proposed method allows for flexible number of nodes, receive antennas, modulated symbols and flexible length of codewords;
(3) A general framework for designing DT-STC with limited feedback was proposed, allowing for flexible system parameters such as the number of transmit/receive antennas, modulated symbols, and the length of codewords, and
(4) a new design method was developed by combining Lloyd's algorithm and the stochastic gradient-descent algorithm to obtain optimal codebook of STCs, particularly for systems with linear minimum-mean-square-error receiver.

- The discrete Fourier transmission spread OFDM (DFTS-OFDM) based single-carrier frequency division multiple access (SC-FDMA) has been widely adopted due to its lower
peak-to-average power ratio (PAPR) of transmit signals compared with OFDM. However, the offset modulation, which has lower PAPR than general modulation, cannot be directly applied into the existing SC-FDMA. In order to overcome such limitations of conventional SC-FDMA, we for the first time investigated cyclic prefixed OQAMOFDM (CP-OQAM-OFDM) based SC-FDMA transmission with adjustable user bandwidth and space-time coding, and obtained the following:-
(1) a CP-OQAM-OFDM transmission technique with unequally-spaced subbands;
(2) a SC-FDMA scheme with the following some valuable features (e.g. a) the transmit signal of each user is offset modulated single-carrier with frequency-domain pulse-shaping; b) the bandwidth of each of user is adjustable; c) the spectral efficiency does not decrease with increasing roll-off factors); and
(3)a joint linear minimum mean square error frequency domain equalization scheme to combat both inter-symbol interference and multiple access interference in frequency selective fading channels, using a priori information with low complexity.

- We considered beamforming strategies in amplified-and-forward (AF) two-way relay channels, where two terminals and the relay are equipped with multiple antennas, and
showed that the optimization problem can be recast as a generalized fractional programing and be solved by using the Dinkelbach-type procedure combined with semidefinite
programming.
Exploitation Route The practical implementation of the proposed schemes is worth further research and development, either by universities or by the wireless communications industry.
Sectors Digital/Communication/Information Technologies (including Software),Electronics

 
Description Global research award
Amount £50,000 (GBP)
Organisation Royal Academy of Engineering 
Sector Learned Society
Country United Kingdom
Start 09/2010 
End 06/2014
 
Description BT 
Organisation BT Group
Department BT Research
Country United Kingdom 
Sector Private 
PI Contribution The research resuts provided significant insights for BT in terms of the benefits and challenges of distributed diversity for future generation wirless systems.
Collaborator Contribution Industry guidance for our reseach effort.
Impact Publications and successor projects.
Start Year 2006
 
Description BT 
Organisation University of York
Country United Kingdom 
Sector Academic/University 
PI Contribution The research resuts provided significant insights for BT in terms of the benefits and challenges of distributed diversity for future generation wirless systems.
Collaborator Contribution Industry guidance for our reseach effort.
Impact Publications and successor projects.
Start Year 2006
 
Description BT 
Organisation Vodafone
Country United Kingdom 
Sector Private 
PI Contribution The research resuts provided significant insights for BT in terms of the benefits and challenges of distributed diversity for future generation wirless systems.
Collaborator Contribution Industry guidance for our reseach effort.
Impact Publications and successor projects.
Start Year 2006