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Cooperation in Cellular Networks

With the rapid development in broadband wireless access technology and explosive growth in demand for new wireless cellular services, it is expected that the next generation cellular network will support a wide variety of communication services with diverse QoS requirements. According to the performance and technical requirements for the 4G networks defined by International Telecommunication Union (ITU), future International Mobile Telecommunications (IMT)-Advanced mobile system will support very high peak data rates for mobile users, up to 1 Gb/s in static and pedestrian environments, and up to 100 Mb/s in high-speed mobile environment. The combination of OFDMA and Cooperative relaying is a promising technique for the emerging fourth generation (4G) networks to satisfy high throughput demand and support heterogeneous communication services with diverse quality-of-service (QoS) requirements. However, efficient relay selection as well as resource allocation are critical in such a network when multiple users and multiple relays are considered.
  • Resource Allocation in Cooperative 4G Cellular Networks

In this work, we focus on a resource allocation problem of maximizing the total achievable throughput for multi-user cooperative OFDMA system considering heterogeneous QoS requirements. Our objective is to develop an optimal joint relay selection, subcarrier assignment and power allocation algorithm as well as some heuristic algorithms to allocate resource efficiently with low computational complexity.

  • Resource Allocation in Cooperative 4G Cellular Networks with Imperfect CSI Information

The benefit of OFDMA and cooperative relaying technologies hinge on the availability of accurate channel state information (CSI) at the resource allocation unit (RAU), which is not the situation in practical networks and needs to be considered in the design of resource allocation schemes. Schemes that are designed based on the assumption that the CSI is perfectly available at the resource allocation unit (RAU) without feedback delay and/or estimation error fail in practical wireless networks for two reasons. First, channel estimations are subject to noise and error that affect the accuracy of the available CSI. Second, in large cells with multiple relay stations and large number of users, reporting the CSI of every subcarrier between all possible pairs (i.e., users and relays, relays and base station, base station and users) could snowball into a huge communication overhead; thus, the zero delay feedback assumption becomes unacceptable. Hence, our work focuses on the development of practical resource allocation schemes accounting for the inaccuracy of CSI.

  • Resource Allocation in Presence of Co-Channel Interference (CCI)

Another challenge of resource allocation schemes in the multi-cell relay based networks is the increase in co-channel interference (CCI) due to inter-cell and intra cell resource reuse. Interference is severe in urban areas due to the large number of base stations and mobile users. In a single cell OFDMA system, CCI caused by adjacent cells can be ignored. However, aggressive frequency reuse with interference coordination techniques is envisioned in 4G system to achieve a much higher spectral efficiency. In this work, we consider multiple cells in our system model in order to reveal the actual performance of a practical system.

  • Coordinated Multi-point in Mobile Communications (CoMP)

Coordinated Multi-Point (CoMP) is one of the promising techniques adopted by new wireless standards like LTE and WiMAX to improve the spectral efficiency of the users, especially users at the cell edges. In this technique, the Base Stations (BSs) are cooperating to apply joint signal processing for the users in different cells. Although this technique shows good performance gains but it still has different challenges. In this research we are trying to investigate these challenges that face the CoMP from being practically deployed.

Current Researchers:

Ahmed Hamza, Md Shamsul Alam.