-The Worldwide Interoperability for Microwave Access (WiMAX) can provide wireless services at high rates even in high mobility, but it can suffer from serious inter-cell interference (ICI) near the cell boundary. To mitigate the ICI problem in the downlink of mobile-WiMAX, we consider combined use of interference avoidance and cancellation techniques in addition to inter-sector coordination, maximizing the user capacity in a seamless manner. To make the proposed scheme realizable, we maximize the geometry capacity. Simulation results show that the proposed scheme can improve the capacity of users near the cell boundary over the conventional schemes and provide flexibility in resource allocation.
SUMMARYThe institute of electrical and electronics engineers (IEEE) 802.16e is designed to support a wide range of applications with various quality of service requirements. Since MAP signaling overhead can unacceptably be large for voice traffic, IEEE 802.16e suggests the use of multicast sub-MAPs whose messages are encoded according to the channel condition. In this case, it is desirable for the base station to properly choose a modulation and coding set associated with the channel condition. In this letter, we consider the use of an adaptive modulation coding scheme for the multicast sub-MAPs without explicit information on the channel condition. The proposed scheme can achieve the same MAP coverage as the broadcast MAP while minimizing the signaling overhead. Simulation results show that when it is applied to voice-over-internet protocol (VoIP) services, the proposed scheme can significantly enhance the VoIP capacity.
The use of beamforming is effective for users in limited power environments. However, when it is applied to the downlink of a cellular system with universal frequency reuse, users near the sector boundary may experience significant interference from more than one sector. The use of a minimum mean square error (MMSE)-type receiver may not sufficiently cancel out the interference unless a sufficient number of receive antennas are used. In this paper, we consider the use of inter-sector beamforming that cooperates with a neighboring sector in the same cell to mitigate this interference problem in time-division duplex (TDD) environments. The proposed scheme can avoid interference from an adjacent sector in the same cell, while enhancing the transmit array gain by using the TDD reciprocity. The performance of the proposed scheme is analyzed in terms of the output signal-to-interference-plus-noise power ratio (SINR) and the output capacity when applied to an MMSE-type receiver. The beamforming mode can be analytically switched between the inter-sector and the single-sector mode based on the long-term channel information. Finally, the effectiveness of the proposed scheme is verified by computer simulation.
In this paper, we consider the service of voice over wise manner to reduce the signaling overhead [1]. However, it in ternet protocol (VoIP) traffic with the service of non-real time has not supported the power control for VoIP packets, but it has traffic in the mobile WiMAX system. VoIP traffic is delay-sensitive supported only AMC [7], [8]. Moreover, it has not considered and requires transmission at an almost constant rate. As a consequence, it may require a large amount of resource when the link adaptation for concurrent transmission of VoIP and users are in poor channel condition, leading to resource outage non-real time traffic (NRT) such as web browsing. In this paper, problem. To alleviate this problem, we consider the allocation of we consider a link adaptation scheme for the concurrent power according to the VoIP traffic load as well as the channel transmission of VoIP and NRT traffic with the use of AMC and condition. When the VoIP traffic is fully loaded, the power is multicast power control. To enhance the system capacity for the allocated to maximize the VoIP capacity. Otherwise, it is allocated service of mixed traffic, we consider the power control to maximize the data throughput. Finally, the performance of the proposed scheme is verified by computer simulation. according to the VoIP traffic load. When the VoIP traffic is fully loaded, the proposed scheme allocates the power to maximize Keywords-IEEE 802.16e; multicast; OFDMA; power control; the VoIP capacity. Otherwise, it allocates the power to maximize the data throughput. Furthermore, it differently VoIP; WiMAX
The use of statistical eigen-beamforming is effective in spatially correlated fading environments, but it may suffer from interference near the sector boundary when applied to the downlink with universal frequency reuse. This interference effect may not sufficiently be handled by a minimum mean square error (MMSE) receiver unless a sufficient number of receive antennas are employed. In this paper, we consider the use of multi-sector beamforming that cooperates with a neighboring sector in the same cell to mitigate this interference problem. By exploiting long-term channel state information (CSI), the proposed scheme can obtain transmit array gain without the use of instantaneous CSI, while avoiding interference from the adjacent cooperating sector. The performance of the proposed scheme is analyzed with combined use of an MMSE receiver and verified by computer simulation.
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