User relay assisted traffic shifting in LTE-advanced systems

In order to deal with uneven load distribution, mobility load balancing adjusts the handover region to shift edge users from a hot-spot cell to the less-loaded neighbouring cells. However, shifted users suffer the reduced signal power from neighbouring cells, which may result in link quality degradation. This paper employs a user relaying model and proposes a user relay assisted traffic shifting (URTS) scheme to deal with the above problem. In URTS, a shifted user selects a suitable non-active user as relay user to forward data, thus enhancing the link quality of the shifted user. Since the user relaying model consumes relay user’s energy, a utility function is designed in relay selection to reach a trade-off between the shifted user’s link quality improvement and the relay user’s energy consumption. Simulation results show that URTS scheme could improve SINR and throughput of shifted users. Also, URTS scheme keeps the cost of relay user’s energy consumption at an acceptable level

Decentralized Fair Scheduling in Two-Hop Relay-Assisted Cognitive OFDMA Systems

In this paper, we consider a two-hop relay-assisted cognitive downlink OFDMA system (named as secondary system) dynamically accessing a spectrum licensed to a primary network, thereby improving the efficiency of spectrum usage. A cluster-based relay-assisted architecture is proposed for the secondary system, where relay stations are employed for minimizing the interference to the users in the primary network and achieving fairness for cell-edge users. Based on this architecture, an asymptotically optimal solution is derived for jointly controlling data rates, transmission power, and subchannel allocation to optimize the average weighted sum goodput where the proportional fair scheduling (PFS) is included as a special case. This solution supports decentralized implementation, requires small communication overhead, and is robust against imperfect channel state information at the transmitter (CSIT) and sensing measurement. The proposed solution achieves significant throughput gains and better user-fairness compared with the existing designs. Finally, we derived a simple and asymptotically optimal scheduling solution as well as the associated closed-form performance under the proportional fair scheduling for a large number of users. The system throughput is shown to be $\mathcal{O}\left(N(1-q_p)(1-q_p^N)\ln\ln K_c\right)$, where $K_c$ is the number of users in one cluster, $N$ is the number of subchannels and $q_p$ is the active probability of primary users.Comment: 29 pages, 9 figures, IEEE JOURNAL OF SELECTED TOPICS IN SIGNAL PROCESSIN

CoMP Aware Radio Resource Management in Integrated PON-OFDM Network

Radio resource management (RRM) is an important component of a mobile wireless network that efficiently utilizes the limited radio resources such as spectrum, transmission power, and network infrastructure. Unfortunately, current RRM schemes do not support cooperative multiple point (CoMP), a promising technology that extends coverage, increases capacity, and improves the spectral efficiency of the next generation broadband network, i.e., 4G network. Specifically, to coordinate with CoMP, a RRM scheme should be aware of three main properties of CoMP - cooperative transmitting information, coordinated scheduling transmission, and single interference noise ratio (SINR) improvement. However, few of the existing RRM schemes consider these properties, since they were designed based on the conventional mobile data networks without CoMP technology. In this dissertation, I present a series of new CoMP aware RRM schemes for ensuring users' throughput and maximizing network capacity in an integrated PON-OFDM network, which is a norm of the 4G network and can best implement the CoMP technology. I call the PON-OFDM network with CoMP a CoMP Network (CoMPNet). I provide two classes of RRM schemes for two practical CoMP technologies, cooperative transmission (CT) and coordinated scheduling (CoS), respectively. In the first class, I propose two groups of RRM schemes using the CT technology. In the first group, three OFDM-TDMA based RRM schemes are designed for three different users' moving speeds. The objective of these schemes is to minimize time slot consumption. The RRM schemes in the third group are contrived for an OFDM-FDMA based CoMPNet. I provide four linear programming (LP) based optimal schemes, one for minimizing bandwidth usage, one for minimizing transmission power consumption, and two for balancing resource costs. An optimized resource allocation solution can be obtained by flexibly choosing one of the schemes according to network load. In the second class, I present a sub-optimal RRM scheme for an OFDM-FDMA based CoMPNet. The CoS technology is applied for ICI mitigation. I formulate the system optimal task into constrained optimization problems for maximizing network capacity. To improve the computation efficiency, fast yet effective heuristic schemes are introduced for divide-and-conquer. The proposed heuristic schemes are featured by CoS based timeslots/subcarriers assignment mechanisms, which are further incorporated with intelligent power control schemes. Through simulations, I study the proposed RRM schemes performances and discuss the effect of the CoMP technology. The performance benefits of CoMP on bandwidth saving and capacity increasing are shown by comparing the new schemes with the conventional schemes without CoMP

Self-Organising Load Balancing for OFDMA Cellular Networks

In this thesis, self-organising load balancing is investigated to deal with the uneven load distribution in OFDMA based cellular networks. In single-hop cellular networks, a self- organising cluster-based cooperative load balancing (CCLB) scheme is proposed to overcome the ‘virtual partner’ and the ‘aggravating load’ problems confronted in the conventional mobility load balancing schemes. Theoretical analysis and simulation results show that the proposed scheme can effectively reduce the call blocking probability, the handover failure rate, and the hot-spot cell’s load. The proposed CCLB scheme consists of two stages: partner cell selection and traffic shifting. In the partner cell selection stage, a user-vote assisted clustering algorithm is proposed, which jointly considers the users’ channel condition and the surrounding cells’ load. This algorithm can select appropriate neighbouring cells as partners to construct the load balancing cluster, and deal with the ‘virtual partner’ problem. In the traffic shifting stage, a relative load response model (RLRM) is designed. RLRM coordinates multiple hot-spot cells’ shifting traffic towards their public partner, thus mitigating the ‘aggravating load’ problem of the public partner. Moreover, a traffic offloading optimisation algorithm is proposed to balance the hot-spot cell’s load within the load balancing cluster and to minimise its partners’ average call blocking probability. The CCLB scheme is modified to apply in multi-hop cellular networks with relays deployed. Both fixed relay and mobile user relay scenarios are considered. For fixed relay cellular networks, a relay-level user shifting algorithm is proposed. This algorithm jointly considers users’ channel condition and spectrum usage of fixed relay, in order to reduce the handover failure rate and deal with the ‘aggravating load’ problem of fixed relay. In the mobile user relay scenario, the user relaying assisted traffic shifting algorithm is proposed to improve the link quality of shifted edge users, which brings about an increase in the achievable rate of shifted edge users and decrease in the handover failure rate