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For wireless communications, the multiple‐input multiple‐output (MIMO) system efficiently makes use of the spectrum and enhances the transmission throughput. In this work, the maximum‐likelihood (ML) detection for the MIMO system is studied, and two ML detection algorithms are first considered for the MIMO system, including the sphere decoding (SD) algorithm and an algorithm based on differential metrics (DMs). Each of the two algorithms has its advantages and disadvantages. The two algorithms are first modified such that they are based on the same signal model. Then, a new ML detection algorithm is proposed for the MIMO system based on the hybrid operation of the two modified algorithms on the tree search process, in which both the branch‐and‐bound principle and indicative functions are applied to remove unnecessary searches. The proposed algorithm can attain the ML detection with lower average complexity over low and high ranges of signal‐to‐noise ratio (SNR), as the authors verify by simulations. The proposed ML detection can also generate soft output, and anti‐phase sequences are exploited to further reduce the complexity. [ABSTRACT FROM AUTHOR]

This paper studies a resource allocation scheme and precoding design to increase the number of quality of service (QoS)-satisfied user equipments (UEs) for multicell multiuser multiple-input-multiple-output downlink systems. The main challenge in such multicell systems is the co-channel interference, including intra-user interference (IUI) and inter-cell interference (ICI). To deal with both IUI and ICI, most conventional schemes aim to maximize the signal to interference plus noise ratio or throughputs through enormous channel state information (CSI) exchange among base stations. In order to avoid such tremendous overhead, this work proposes a novel framework, containing a distributed subcarrier assignment and a block diagonalization (BD) precoding, to cope with both types of interferences based on limited exchanged information of subcarrier-assignment and local CSIs (channel gains). In the subcarrier-assignment process, each sector's base station independently assigns a subset of the served UEs to be served over the subcarrier. The channel gains of a particular subcarrier hold a semi-orthogonal property for that subset. Then, on the basis of limited exchanges of information, a BD-type precoding is presented to completely eliminate all IUI and suppress the major part of the leakage interference to the adjacent sectors by exploiting principal component analysis. The simulation results indicate that the proposed framework can provide more QoS-satisfied UEs than that obtained in a previous work. [ABSTRACT FROM AUTHOR]

To increase spectrum efficiency, the radio resource management with frequency reuse factor = 1 is usually adopted in multi-cell orthogonal frequency division multiple access systems. Such a reuse-one strategy results in severe co-channel interference, especially penalizing mobile users near the cell border. This paper presents an effective subcarrier-assignment algorithm to mitigate the co-channel interference for multi-cell orthogonal frequency division multiple access downlink systems. The proposed algorithm consists of an initial assignment phase and a compensation phase. In the first phase, each subcarrier is assigned to mobile users with higher channel gains and lower mutual co-channel interferences. The second phase further compensates mobile users who do not get adequate resources to meet the requirement of quality of service in the first phase. System simulation results reveal that the proposed algorithm can significantly improve the number of QoS-satisfied users compared with previous used scheme. [ABSTRACT FROM AUTHOR]

In this paper, we propose a cross routing and MAC QoS protocol design, named Signal-to-Interference-plus-Noise-Ratio and Quality-of-Service (SINR-QoS), for wireless ad hoc networks. SINR-QoS is spatial-reuse time division multiple access (STDMA)-based. Unlike most of the conventional approaches, SINR-QoS manages the spatial reuse based on SINR. When a data flow with end-to-end throughput requirement arrives, the routing part of SINR-QoS, called SINR-QoS-routing (SQ-routing), determines a route, and assigns STDMA slots, transmission rate, and transmission power for each link on the route. The assignment is SINR-based, and thus requires some SINR-related information to coordinate the co-channel interference. Hence, the MAC part of SINR-QoS, called SINR-QoS-MAC (SQ-MAC), is proposed for nodes to acquire and update the SINR-related information. With the specific design of SQ-MAC, SINR-QoS can precisely manage the spatial reuse without explicit channel-gain exchange between interfering neighbors. Simulation results show SINR-QoS outperforms the existing QoS approaches in both total end-to-end throughput and reliability. [ABSTRACT FROM AUTHOR]

This paper considers the problem of joint topologytransparent scheduling (TTS) and quality-of-service (QoS) routing in ad hoc networks and presents a joint scheme for the problem. Due to its ability to guarantee single-hop QoS support, TTS is chosen as the underlying medium-access-control (MAC) protocol. By being built on top of TTS, this paper first designs methods for bandwidth estimation and allocation (BWE and BWA, respectively) to provide QoS support without knowledge of slot status information, and then, estimates and allocates nonassigned eligible bandwidth for best effort (BE) flows. With these bandwidth management methods, this paper proposes a QoS routing protocol for a mixture of QoS and BE flows. Idealized simulation results based on the standard radio model, which ignores external sources of radio interference and protocol inefficiencies, reveal that the proposed joint scheme can provide a reduction of at least 93% in QoS violation rates and a reduction of 78%–89% in control overhead compared with the conventional dynamic source routing (DSR)/IEEE 802.11 technique. A comparison with another conventional technique, i.e., DSR/carrier sense multiple access (CSMA), also reveals that the proposed joint scheme can reduce QoS violation rates by at least 93%. In addition, the proposed joint scheme can provide an increase of 31%–104% in aggregate throughput over two representative QoS routing protocols while achieving a reduction of approximately 93% in QoS violation rates. The performance improvement to be achieved under a realistic radio model is yet to be determined. [ABSTRACT FROM PUBLISHER]

In this paper, we propose and analyze a rapid acquisition loop for a direct-sequence ultrawideband (DS-UWB) system called robust matched-filter acquisition, which is mainly aimed at eliminating the cases of false alarm in signal acquisition. Moreover, we present a study on the acquisition performances of the serial search, conventional matched filter, and robust matched filter in UWB dense multipath environments. The mean acquisition time, the acquisition probability, and the mean number of false alarms are evaluated for CM1-CM4 channel models. We find that the robust matched-filter acquisition provides a significant improvement in performances over the conventional matched-filter algorithm for the specific UWB channel model. [ABSTRACT FROM AUTHOR]

Investigates the combined performance of digital delay-locked loop (DDLL) and automatic gain control (AGC) loop for direct-sequence spread-spectrum systems. Block diagram of the combined DDLL and AGC loop; Loop behavior in the absence and presence of alternating current noise; Effect of AGC on the tracking performance of DDLL.

To be differentiated from the literature, in this paper, we aim to alleviate the impact of pilot contamination (PC) on the massive MIMO systems by cooperatively scheduling users (rather than just assigning) among neighboring cells to share the limited orthogonal pilots. To this end, we develop the multi-cell cooperative scheduling (MCCS) algorithm together with the cooperative scheduling indexes (COSIs) for maximizing the data rate, maximizing the Jain's fairness index and reaching a better tradeoff in-between. For convenience, they are denoted by the COSIs for the CMDR, CMMF and CPF schedulers, respectively. However, its high computational complexity may somehow resists its from practical applications. Thus, a low-complexity cooperative proportional fairness (LC-CPF) algorithm is designed to well approach the MCCS algorithm using the CPF COSI; and at the meantime, the order of computational complexity can be significantly reduced. Moreover, its ability to reach a better tradeoff can still be maintained under the impact of high spectrum-sharing interference. In addition, it is interesting to find that using the proposed cooperative scheduling methods, the open-loop power control mechanism is no longer required for compensating the differences of received signal quality between users. [ABSTRACT FROM AUTHOR]