In this paper, we propose a concept of parasitic communication system via relaying. The proposed system is suitable for improving the throughput of some users who are far from the base station or have numerous obstructions in their communication links. In the parasitic communication system, the users communicate to the base station by following the original setting of the standards. Only a slight modification at the retransmission mode is required. Therefore, the proposed approach is backward compatible to several existing systems.

Despite its low-complexity, the zero-forcing receiver is known to suffer from noise enhancement to restore the spatially multiplexed data in a single-user MI MO system. Nevertheless, in the multiuser system, the poor-channel avoidance property of the scheduling technique provides a natural way to overcome the drawback of noise enhancement (Heath et al., 2001). In this paper, we present an analytical framework to evaluate the performance of the zero-forcing receiver operating in the multiuser MIMO system with user scheduling. Using the order statistics technique, we derive closed-form expressions for the sum-rate capacity of the multiuser MIMO system that employs the simple spatial multiplexing at the transmitter and zero-forcing processing at the receiver with a number of scheduling algorithms. These closed-form expressions hold for an arbitrary finite number of users and facilitate efficient numerical evaluations for cases of practical interest. In addition, the tractable analysis provides insight into how the scheduling technique affects the performance of the multiuser MIMO system under scalar feedback and vector feedback. The results are also extended to the case of heterogonous users with unequal average SNR.

In this paper, we present a cross-layer analytical framework to jointly investigate antenna diversity and multiuser scheduling under the generalized Nakagami fading channels. We derive a unified capacity formula for the multiuser scheduling system with different multiple-input multiple-output antenna schemes, including: 1) selective transmission/selective combining (ST/SC); 2) maximum ratio transmission/maximum ratio combining (MRT/MRC); 3) ST/MRC; and 4) space-time block codes (STBC). Our analytical results lead to the following four observations regarding the interplay of multiuser scheduling and antenna diversity. First, the higher the Nakagami fading parameter, the lower the multiuser diversity gain for all the considered antenna schemes. Second, from the standpoint of multiuser scheduling, the multiple antennas with the ST/SC method can be viewed as virtual users to amplify multiuser diversity order. Third, the boosted array gain of the MRT/MRC scheme can compensate the detrimental impact of the reduced amount of fading gain on multiuser scheduling, thereby resulting in greater capacity than the ST/SC method. Last, employing the STBC scheme together with multiuser diversity may cause capacity loss due to the reduced amount of fading gain, but without the supplement of array gain.

Recent studies have revealed that the remarkable capacity improvement resulting from an open-loop multiple-input-multiple-output (MIMO) spatial multiplexing system may come at the sacrifice of degrading link reliability. This tradeoff between antenna multiplexing gain against antenna diversity gain may translate into smaller coverage areas. In this paper, we suggest using the multiuser diversity to replenish the diversity-deficient spatial multiplexing MIMO system. Specifically, we propose a fair scheduling scheme, called the strongest-weakest-normalized-subchannel-first (SWNSF) scheduling, which requires only limited amount of feedback. Our analysis and results indicate that the SWNSF scheduling can significantly increase the coverage of the multiuser MIMO system while further improving the system capacity.

Despite its simplicity, the zero-forcing receiver is known to suffer from noise enhancement to restore the spatially multiplexed data in a point-to-point MIMO system. Nevertheless, in the point-to-multipoint multiuser system, the poor channel avoidance property of the scheduling technique provides a natural way to overcome the drawback of noise enhancement. In this paper, we present an analytical framework to evaluate the performance of the zero-forcing receiver operating in the multiuser MIMO system with scalar feedback scheduling. Using the order statistics technique, we derive closed-form expressions for the achievable throughput of the zero-forcing receiver operating in the multiuser MIMO environment. Our analytical results indicate that the cross-layer cooperation of the simple zero-forcing receiver and scheduling technique can achieve the full capacity of the point-to-point MIMO system.

Recent studies have revealed that the capacity improvement resulting from an open-loop multiple-input-multiple-output (MIMO) spatial multiplexing system may come at the sacrifice of reducing link reliability. The tradeoff of antenna multiplexing gain against antenna diversity gain may lead to smaller cell coverage sizes. In This work, we propose a scheduling scheme, called the strongest-weakest-normalized-subchannel-first (SWNSF) scheduling, to replenish the diversity-deficient MIMO system with multiuser diversity. Our analysis and results indicate that the SWNSF scheduling can significantly increase both cell coverage and system capacity requiring only limited amount of feedback.

This paper presents a cross-layer analytical framework to jointly investigate antenna diversity and multiuser scheduling under the generalized Nakagami fading channels and derives a unified capacity formula for the multiuser scheduling system with different multiple-input multiple-output (MIMO) antenna schemes, including the selective combining (SC), maximum ratio combining (MRC) and space-time block codes (STBC). Our analytical results indicate that, in the presence of multiuser diversity, the multiple antennas with the SC method can be viewed as virtual users to amplify multiuser diversity order, while the MRC scheme can even yield greater capacity than the SC scheme due to the increased array gain. However, applying the STBC method on top of the multiuser scheduling system may lead to capacity loss due to the reduced amount of fading.

This paper presents an analytical framework to evaluate the downlink capacity and fairness performance for high speed wireless data networks from both the physical layer and the network layer perspectives. From the physical layer standpoint, we take into account of propagation loss, log-normal shadowing and Nakagami fading. From the network layer perspective, we model different scheduling policies and the impact of nonuniform traffic intensity of mobile users into our framework. We analyze the joint effects of radio channel impairments, nonuniform traffic intensity and scheduling algorithms on the downlink capacity and fairness performance of wireless data networks based on the developed framework. Our results indicate that it is crucial for wireless scheduling algorithms to consider not only the radio channel impairments, but also the traffic intensity distribution in the whole network.

In this paper, we present a new hierarchical cell system with an underlaid TDD/CDMA microcell and overlaying FDD/CDMA macrocells. With an objective to exploit the underutilized FDD uplink capacity due to traffic asymmetry, the TDD/CDMA microcell is operated within the uplink frequency band of the overlaying FDD/CDMA macrocells. By jointly applying the proposed antenna arrays at the cell site and a new power ratio adjustment technique, we evaluate the outage probabilities of the macrocell and the microcell. From the simulation results, we demonstrate that the full capacity of the TDD/CDMA microcell can be obtained without degrading the performance of FDD/CDMA macrocells.