Possible directions of my work

Possible directions of my work

Communication through intermediate relay splits the channel between source and destination into possibly shorter links, which improves the link quality. At present such technique is used in GSM system, where relay improve the signal strength at shadow zone and outskirts of cells. Cooperation among these relay nodes can combat with harsh multi-path fading and improve reliability of transmission. In the original proposals of cooperative relaying, single antenna wireless terminals were considered. Recently, researchers are proposing multi-antenna infrastructure based relays for enhancing the performance of cooperative relaying. However, several important issues which are not addressed till now. I am planning to work on such issues which are briefly outlined below:

System modelling taking inference into consideration: In network scenario, cooperative relay system can suffer from co-channel and adjacent channel interference. Hence, effect of this interference need be addressed in future.

Power Optimization based on link condition: Wireless nodes generally have limited battery power. If relay based systems have some feedback mechanism then power can be allocated based on link condition. Such dynamic allocation of power may save battery power or boost the data transfer rate and hence an important area to be investigated.

Full duplex operation of relays: Relay operation in half-duplex mode creates system bandwidth expansion. Full-duplex relay operating in single frequency can solve this problem. Hence, further investigation is necessary for full-duplex relay operation.

Spectral efficiencies: Orthogonal transmission from relays to receiver in different time slots affects the spectrum efficiency. Relays can interact with the receiver using orthogonal codes to avoid bandwidth expansion. Therefore, issues of orthogonal code design for distributed relay nodes may be addressed in future.

Complexity performance trade off: Relays can process the signal in non-regenerative or regenerative mode depending on their functionality. Non-regenerative mode of operation puts less processing burden as compared to regenerative mode of operation, hence often preferred when complexity and/or latency are important issues. Scope exists in future for non-regenerative mode of relay operation. Noise amplification is a major issue in non-regenerative mode of operation.

Multi-hop communication: The research community has increased its attention towards wireless multi-hop communication due to it envisioned application of Ad-Hoc networks, sensor network and range-extension of cellular networks.

Modelling of relay link in various environments: Radio propagation suffers with path loss, shadowing and multi-path fading which depends on regional geography. Statistical behaviour of various propagation environments is available in literatures. Relay link can be modelled in such propagation environment, which will be possible extension of my work.

Diversity combining techniques for relay system: System model considered here processed the signal with the help of selection combining receivers or maximum ratio combining receivers. In future, other type of diversity combining techniques such as equal gain combining, switch combining etc. can be incorporated in relay based system.

Power Optimization: Relays are generally wireless nodes and have limited battery power. If such system supports some feedback mechanism then power can be allocated based on link condition. Such dynamic allocation of power may save battery power or boost the data transfer rate and hence can become important area to be investigated.

Relay Selection: In the present state of art, wireless relay nodes are half-duplex in nature. Participation of large number of relay increase the diversity order but spectrum efficiency of system may suffer. Therefore, how to select the nodes and how many nodes should be selected to optimize the performance in terms of rate and reliability is an interesting field of research.

Spectrum Efficiency: Orthogonal transmission from relays to receiver in TDMA mode can affects the spectrum efficiency. Relay can interact with the receiver in CDMA mode which avoids bandwidth expansion. Therefore, orthogonal code design for distributed relay node may be the possible area for research.

Complexity performance Trade-off: Relays can process the signal in non-regenerative (analog) or regenerative (digital) mode depending on their functionality. Non-regenerative type relay simply amplifies and forwards the received signal, while in the later, the relay decodes, encodes, and forwards the received signal. Despite of noise propagation, amplify and forward (AF) mode of operation puts less processing burden on the relay and, hence is often preferred when complexity and/or latency issues are important. Adaptive protocol with DF scheme have a drawback that relay remains silent if received SNR at relay is poor, hence relay remain silent and diversity order of system reduces. Relay operate in DF mode if received SNR at relay is above the particular threshold and switched to AF mode if it is below the particular value may solve the problem, so extension of my work in this way may be interesting.

Node cooperation with cross-Layer design: Node cooperation is a powerful technique to improve the performance of wireless sensor network. Sensor nodes are powered by small battery that may not be recharged easily. So reducing energy consumption is important issue for such type of network. Protocol layering in network design provides modularity for network protocols that facilitates standardization and implementation. Unfortunately, layering precludes the benefits of joint optimization across protocol layers hence precious battery power cannot be efficiently utilized. In this regard, it would be interesting to investigate cross-layer optimization of my work.

Wireless multi-hop communication: The research community has increased its attention towards wireless multi-hop communication due to it envisioned application of Ad-Hoc networks, sensor network and range-extension of cellular networks. This work generally investigates two-hop communication which may be extended for multi-hop communication.

Cooperation in interfering channel: Relay network have low spectrum efficiency due to half-duplex nature of relay terminals. Spectrum efficiency of such network can be improved if spatially distributed relay can transmit in same time-slot and we can reuse the time-slot by simultaneous transmission. In this case interfering signal received by receiver can be minimized by allowing largely separated active relay operation in same time-slot or incorporation of interference compensation techniques like dirty paper coding is possible extension of my work.      

Bidirectional user cooperation: In this work, we are assuming that relay terminals do not have their own data and they are just forwarding the data received from source. In user cooperation, users terminal not only have to transmit its own data but also other users data by sharing some of the resources. Extension of my work for bidirectional user cooperation may be interesting.

Base station cooperation: In traditional cellular system, user terminals communicate with a parent base station. Users near the outskirts of cell can see other neighbouring base stations and become an active source for generating interfering signals. To overcome this problem, neighbouring base stations can also cooperate with parent base station and perform joint decoding of received signals. The work presented for relay cooperation, can be extended for base station cooperation.