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Interference coordination is a critical enabler of heterogeneous networks. In this paper we present a scheduling cooperation scheme that coordinates the resource allocation and user assignment across layers. The proposed scheme focuses on mitigating the interference generated by macro-associated users in the proximity of small cells by exchanging the information of user assignment on the severely-interfered...
In this paper, the hardware realization of UMTS femtocell modem with multiuser interference cancellation technology is presented for the first time. The design and implementation are compliant with the 3GPP/UMTS standard for Wideband Code-Division Multiple Access (WCDMA) baseband air-interface and exceeds 3GPP minimum requirements by 2dB in Additive White Gaussian Noise (AWGN) environment. The modem...
In this paper, we investigate efficient beamforming schemes for downlink broadcast channels of MIMO systems. Optimal solution to this problem is known to be infeasible due to the prohibitive complexity and recent research focuses on suboptimal approaches with reduced complexity. We first present a progressive beamforming method that maximizes the net gain in sum throughput for newly added users and...
Capacity and Coverage are the two major concerns for the wireless operators to deploy cellular networks. This paper investigates the uplink capacity and coverage of relay-assisted UMTS network when multiuser detection techniques are employed at both macrocell base station (BS) and relay station (RS). A hierarchical geometric system model is used where the fixed relay stations are deployed within the...
In this paper, we investigate downlink coordinated multi-point (CoMP) schemes for generic wireless communication systems. We propose a suboptimal joint transmission (JT) algorithm based on the alignment of signal vectors received from coordinating base stations. Signal alignment at the receive end of terminals imposes linear constraints between transmitted signals of cooperating cells. The capacity-achieving...
Since the Quality of Experience (QoE) metric directly reflects the subjective experiences of users, the resource allocation techniques with the objective to improve QoE instead of conventional metrics are efficient in resource utilization. This kind of techniques can avoid wasting resources in providing perfect objective metric which may have little or even no effect on user experience. This paper...
Multicell collaboration is considered for power allocation in OFDMA downlink to mitigate the intercell interference. We propose a coordination approach to maximize the sum utility of a cluster of co-channel users by properly configuring user transmit power in local cells. In particular, we employ the well-known $\alpha$-PF metric as the utility function to accounts for the fairness between users in...
More and more CPU-based SDR systems appear in recent two years. Such system requires high speed real-time signal processing. In this paper, we present our effort on the speed optimization of Turbo decoder, the most computation-demanding module in all baseband modules. We jointly consider the algorithm parallelism and the processor architecture. Single Instruction Multiple Data (SIMD) instruction is...
In this paper, we address the intercell interference (ICI) in multi-cell networks by dynamically sharing the spectrum through collaboration between base stations. Throughput marginal utility (TMU) is utilized in resource allocation, and a theoretic framework based on TMU optimization is formulated. A distributed power allocation scheme is developed to exploit the average channel statistics of other...
In this paper, a two-tier UMTS network is considered where a large number of randomly deployed Wideband Code Division Multiple Access (WCDMA) femtocells are laid under macrocells where the spectrum is shared. The co-channel interference between the cells may be a potential limiting factor for the system. We study the uplink of this hybrid network, and identify the critical scenarios that give rise...
It is well-known that wireless scheduling algorithm could exploit multi-user diversity to enhance the network capacity. With multiple transmit/receive antennas, there are additional degrees of freedom which could deliver either spatial multiplexing gain and/or spatial diversity gain. With cross layer scheduling, there is also multi-user selection diversity which contributes to both network capacity...
In the multi-cell environment, the approaches that are suitable for the single cell scenario may cause excessive interference to other cells and become suboptimal. In this paper, we present a number of receiver-centric power allocation schemes that take into account the detrimental impact of allocated resources to the neighboring cells, and use it as a guideline in determining the appropriate power...
Recently interleaved division multiple access (IDMA) has been proposed as an enhancement for 3GPP wireless broadband standards. Timing synchronisation in an IDMA system must take place in conjunction with signal detection and decoding. This paper compares an iterative timing recovery technique with a conventional timing recovery approach for IDMA systems in the uplink. Under high multiple access interference...
This paper proposes an analytical model to investigate the impact of interference on the uplink capacity and coverage in a WCDMA network where macrocell and femtocells co-exist. Geometric modeling for the hierarchical system is used where the randomly deployed femtocells are within the planned macrocells' topology. The interference effects among femtocells and between femtocells and macrocells are...
In this letter, we propose a successive multiuser detector (SMUD) for contention based OFDMA ranging channel compliant to the IEEE 802.16 (WiMAX) standard. A ranging channel consists of a set of subcarriers in specific time slots shared by multiple users, so the multiple access interference (MAI) limits the performance of ranging detectors. Different from existing methods that treat the MAI as noise,...
In orthogonal frequency-division multiplexing (OFDM) systems, the integer part of carrier frequency offset (CFO) as a multiple of subcarrier spacing needs to be estimated from the frequency-domain signal. The performance of the autocorrelation based method is quite poor, while the channel knowledge based method is too complex for hardware real-time implementation. To provide improved tradeoffs between...
This paper studies fractional carrier frequency offset (CFO) estimation for orthogonal frequency-division multiplexing (OFDM) systems. In the IEEE 802.16 (WiMAX) standard, a training symbol structure with three highly correlated but not identical segments is specified. The existing CFO estimation methods require the segments in the training symbol to be identical, so cannot work for the generalized...
In this paper, we develop a rate allocation scheme for interleave-division multiple-access (IDMA) systems with iterative decoding. We use a fully-analytical approach to predict the performance of the scheme and propose a modified linear programming method to design the rate profile. Numerical results show that with just repetition coding and rate allocation, the performance of the scheme is only about...
Markov Chain Monte Carlo (MCMC) method applied as Multiple-Input-Multiple-Output (MIMO) detector has shown near capacity performance. However, the conventional MCMC method suffers from an error floor in the high signal-to-noise (SNR) region. This paper proposes a novel robust reduced-state-space MCMC (RSS-MCMC) method, which utilizes the a priori information for the first time to qualify the reliable...
To alleviate the high peak-to-average power ratio (PAPR), high complexity in user terminal and sensitivity to carrier frequency offset (CFO) problems in current OFDMA systems, a Quadrature OFDM (Q-OFDMA) system has been recently proposed in the single-input single-output environment. In this paper we investigate the realization of multi-input multioutput (MIMO) diversity- and capacity- oriented methods...
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