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Free probability theory, which has became a main branch of random matrix theory, is a valuable tool for describing the asymptotic behavior of multiple systems, especially for large random matrices. In this paper, using free probability theory, a new cooperative scheme for spectrum sensing is proposed, which shows how asymptotic free behavior of random matrices and the property of Wishart distribution...
Interference cancellation (IC) techniques yielding significant capacity gains are presented in this paper for CDMA2000 lx base station receiver. In addition to performance gain from conventional IC, hybrid ARQ gain is achieved effectively without interlaced transmission or feedback on the forward link (FL). A new definition of CDMA capacity, based on equivalent load, is introduced to allow a fair...
For downlink transmission in a multiuser multiple-input multiple-output (MIMO) communication system, quantized Channel State Information (CSI) is fed back to the base station in an uplink channel of finite rate. The quantized CSI is obtained via Channel Vector Quantization (CVQ) of the so-called composite channel vector, i.e., the product of the channel matrix and an estimation of the receive filter,...
In this work we consider the optimization of the power assigned to the user streams, in a coordinated base station downlink environment, when zero-forcing is employed to remove interference among users. Two schemes based on the waterfilling technique are proposed and compared to the optimal solution, which can be obtained numerically, by using convex optimization. We show that the proposed schemes...
Mobile location estimation via the use of a spatially-dependent signal database is of growing importance. However, this location estimation method usually requires an a priori experimental measurement campaign. To overcome this drawback we propose here a new method of location estimation via the real-time creation of a virtual signal database. The virtual database is created on-demand by an optimized...
In this paper, a new opportunistic feedback and user selection protocol is proposed for the multiple antenna downlink. The proposed scheme uses the structure of zero-forcing dirty paper coding (DPC) at the transmitter and selects users using a contention-based feedback channel. The user selection procedure is divided into stages and within each stage, a user is selected for one spatial channel (defined...
IEEE 802.22 wireless regional area network (WRAN) is an emerging cognitive radio-based system. One of the major challenges for WRANs is how to efficiently schedule both channel sensing and data transmission for multiple adjacent WRAN cells. This challenge is known as coexistence problem. In this paper, we propose four schemes that aim at reducing the coexistence-problem effect. These schemes are based...
This paper analyzes the carrier-to-interference ratio of the so-called shotgun cellular system (SCS). In the SCS, base-stations are placed randomly according to a two-dimensional Poisson point process. Such a system can model a dense cellular or wireless data network deployment, where the base station locations end up being close to random due to constraints other than optimal coverage. The SCS is...
This paper considers downlink multiantenna communication with base stations that perform cooperative precoding in a distributed fashion. Most previous work in the area has assumed that transmitters have common knowledge of both data symbols of all users and full or partial channel state information (CSI). Herein, we assume that each base station only has local CSI, either instantaneous or statistical...
Dense frequency reuse makes the intercell interference control a crucial issue in cellular systems. Due to large signalling overhead, multicell processing and resource scheduling are not practicable solutions, at least today. We propose a decentralized transmission scheduling scheme where each base station exploits the knowledge of the intercell interference to locally allocate the resources. The...
Average and outage capacities for nonidentical two-user opportunistic scheduling for wireless network coding (OWNC) are derived in this paper. Nonidentical user case represents a more realistic scenario in which two users have different average signal-to-noise ratio (SNR). Our derived analytical results corroborate with the simulation results in the performance evaluation of OWNC. Insight on the performance...
The deployment of large-scale wireless sensor networks presents major challenges whose solution requires the design and development of robust and time-efficient protocols. In this work, we focus on the design of an efficient and robust protocol aiming to rapidly configure highly populated networks. Our main effort goes towards the definition of a fast collision resolution protocol for conveying the...
We propose an intercell downlink orthogonal frequency division multiple access (OFDMA) scheduling technique in a sectorized cellular network. Adjacent sectors from neighboring cells form a cluster and each OFDMA resource block is allocated to the rate-maximizing sector. Compared to a cellular network that uses conventional fractional frequency reuse (FFR) technique, our proposed system requires only...
The downlink capacity of cellular networks is known to be strongly limited by inter-cell interference. In order to mitigate this interference, a number of frequency reuse schemes have recently been proposed. In this paper, we compare the potential capacity gains of these schemes accounting for the random nature of traffic.
User selection for multiuser linear precoding in broadcast channel is investigated in this paper. Assuming complete knowledge of channel state information at the transmitter, new user selection algorithms are introduced using minimum mean square error criterion. A novel iterative user selection is proposed offering a flexible performance-complexity tradeoff. New algorithms are also developed for orthogonal...
In a multihop cellular network, mobile terminals are able to transmit directly to other mobile terminals allowing them to lower their maximum transmission power and use other terminals as relays to forward traffic towards the base station. However, a large amount of interference is created near the base station because all traffic either emanates or is destined to the base station making it the capacity...
We propose a new limited feedback scheme for the downlink of multiuser MIMO OFDM systems based on fixed linear beamforming, i.e. the linear beamforming vectors are chosen from a fixed transmit codebook. The proposed feedback method allows the base station to uniformly approximate all multiuser rates for any selection of users and any combination of beamforming vectors defined by the transmit codebook;...
An optimized algorithm and a corresponding reconfigurable architecture for computing Zadoff-Chu (ZC) complex sequence elements based on the CORDIC algorithm are proposed. The algorithm computes ZC-sequence elements both in time domain and frequency domain using a simple duality relationship. Algorithm transforms are employed to compute the elements recursively and eliminate multipliers with nonconstant...
In this paper, we introduce a novel queue management technique for the buffer space at the base station of infrastructure 802.11 networks that considers mobile user's receiving characteristics. The maximum amount of the base station buffer that can be used by a given flow is updated proportionally to RTT, measured at the mobile nodes and sent to the base station my the mean of link layer acknowledgements...
The capacity of today's cellular mobile communications systems is mainly limited by inter-cell interference. Multi-cell joint transmission or joint detection schemes are means to overcome this limitation and to actively exploit signal propagation across cell borders rather than treating it as noise. In the cellular uplink, messages of multiple terminals can be detected jointly by cooperating base...
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