| 1. |
- Girnyk, Maksym, 1984-, et al.
(författare)
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On the asymptotic sum-rate of the relay-assisted amplify-and-forward cognitive MIMO channel
- 2012
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Ingår i: Personal Indoor and Mobile Radio Communications (PIMRC), 2012 IEEE 23rd International Symposium on. - : IEEE. - 9781467325691 ; , s. 709-714
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Konferensbidrag (refereegranskat)abstract
- This paper studies the asymptotic sum-rate of the primary network within the relay-assisted multi-antenna cognitive radio system performing amplify-and-forward relaying. The achievable sum-rates are derived in the large-system limit by means of the replica method. A closed-form expression for the sum-rate of the primary network is obtained for large antenna arrays as a function of parameters obtained by solving a set of fixed-point equations. Numerical simulations confirm the validity of the results even for systems with only a few antennas at each terminal.
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| 2. |
- Hussain, Iqbal, et al.
(författare)
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Design of Spatially-Coupled Rateless Codes
- 2012
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Ingår i: 2012 IEEE 23rd International Symposium on Personal, Indoor and Mobile Radio Communications - (PIMRC). - : IEEE. - 9781467325691 ; , s. 1913-1918
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Konferensbidrag (refereegranskat)abstract
- We investigate the design and performance of spatially-coupled rateless codes. A modified encoding process is introduced for spatially-coupled Luby Transform (SCLT) codes which leads to an almost regular variable-node degree distribution at the encoding graph. The proposed SCLT codes outperform its counterparts significantly over binary erasure channels, particularly in the erasure floor region. To further improve the erasure floor performance, the approach of spatial coupling is then extended to Raptor codes by concatenating a high-rate pre-coder to the SCLT codes. It is shown that the spatial coupling improves the convergence threshold of Raptor codes. Different ensembles of spatially-coupled Raptor codes are constructed depending on whether pre-coders and/or LT codes are spatially-coupled. The performance of different ensembles of spatially-coupled Raptor codes is then evaluated and compared based on density evolution, leading to an improved spatially-coupled Raptor code in terms of convergence threshold and lower complexity.
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| 3. |
- Lakshmana, Tilak Rajesh, 1980, et al.
(författare)
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On the Potential of Broadcast CSI for Opportunistic Coordinated Multi-Point Transmission
- 2012
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Ingår i: IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC. - 9781467325691 ; , s. 1262-1267
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Konferensbidrag (refereegranskat)abstract
- Coordinated Multi-Point transmission is a promising technique to improve the performance of the users at the cell-edge. To achieve this, in case of a centralized approach, users need to unicast the quantized channel state information (CSI), typically to the anchor base station (BS), and then each BS forwards this information to a central coordination node for precoding and scheduling. In the case of a decentralized approach, users broadcast the quantized CSI such that the coordinating BSs could simultaneously receive the CSI. The advantage of a decentralized approach is that it does not require a central coordination node, thereby not imposing stringent latency constraints on the backhaul. The CSI transmission over the erroneous feedback channel in the uplink gives rise to precoding loss and scheduling loss. In the decentralized framework, the feedback errors could result in BSs receiving a different version of the CSI. In this work, we propose a decentralized opportunistic scheduling approach, which only requires a minimal sharing of scheduling information between BSs. The results show that the sum rate achieved with the proposed method is comparable to that of the centralized approach even when there is a high bit error probability introduced by the feedback channel. We also show that when the bit error probabilities in the feedback channel are less than 10^{-4}, the decentralized approach achieves the sum rate of the centralized approach.
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| 4. |
- Li, Jingya, 1986, et al.
(författare)
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Performance evaluation of coordinated multi-point transmission schemes with predicted CSI
- 2012
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Ingår i: IEEE Conference on Personal, Indoor and Mobile Radio Communications, PIMRC, Sydney, Australien. - 9781467325691 ; , s. 1055-1060
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Konferensbidrag (refereegranskat)abstract
- Coordinated multi-point (CoMP) transmission is considered as an efficient technique to improve cell-edge performance as well as system spectrum efficiency. In CoMP-enabled systems, a cluster of coordinated base stations (BSs) are typically assumed to be connected to a control unit (CU) via backhaul links, and the provided performance gain relies heavily on the quality of the channel state information (CSI) available at the CU side. In this paper, we consider the downlink of a CoMP cluster and compare three different CoMP transmission schemes: zero-forcing coherent joint transmission, non-coherent joint transmission and coordinated scheduling. Moreover, for each of the analyzed schemes, the performance in terms of average sum rate of the CoMP cluster is studied with predicted CSI, considering the effects of the feedback and backhaul latency, as well as the user mobility. Compared to zero-forcing coherent joint transmission, we show that non-coherent joint transmission and coordinated scheduling are more robust to channel uncertainty. In addition, depending on the latency, user mobility and user locations, different schemes would achieve the highest average sum rate performance. Hence, a system could switch between the transmission schemes to improve the sum rate.
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| 5. |
- Moghadam, Nima N., 1986-, et al.
(författare)
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Correlation of distortion noise between the branches of MIMO transmit antennas
- 2012
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Ingår i: Personal Indoor and Mobile Radio Communications (PIMRC), 2012 IEEE 23rd International Symposium on. - : IEEE. - 9781467325691 ; , s. 2079-2084
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Konferensbidrag (refereegranskat)abstract
- Despite the tremendous research effort spent on MIMO systems - very few papers address the impact of hardware imperfections. In this paper we analyze the distortion noise of the transmitter branches of a MIMO transmitter. In particular we analyze the cross-correlation of the distortion noises for the case that the transmitted signals are correlated. This case arises when there is just a single stream being transmitted with beamforming or in the case of multiple streams and linear precoding. We analyze the problem in two ways: using analytical derivations and using measurements on our testbed. In the analytical case we assume a transmitter impaired by a 3rd order non-linearity. For this scenario we find that the absolute correlation coefficient of the distortion noises is given by the absolute value of the correlation coefficients of the input signals to the power of three, while the phase is the same as that of the input signal. Our measurements also show good agreement between measurements and analytical results. It seems to suggest that the distortion noises can be regarded as practically independent whenever there are two or more modulation streams being transmitted (spatial multiplexing). In a single-stream scenario, the distortion noise will tend to have the same spatial distribution as the desired signal.
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| 6. |
- Shalmashi, Serveh, et al.
(författare)
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Performance analysis of relay-assisted cognitive radio systems with superposition coding
- 2012
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Ingår i: Proceedings of the IEEE 23rd International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC). - : IEEE. - 9781467325691 ; , s. 1226-1231
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Konferensbidrag (refereegranskat)abstract
- We study the problem of relay selection in a cooperative cognitive radio system in which a secondary transmitter can act as a relay for the primary transmitter in order to maximize the primary user's gain. Moreover, we take into account that the secondary users may have certain quality-of-service (QoS) requirements which need to be satisfied. In the cooperative scenario of a cognitive radio system, the primary user should have an incentive to allow the secondary user to transmit in its licensed band. At the same time, the secondary user should be able to transmit its own data with the required QoS in order to be willing to help the primary user's performance by relaying its data. Hence, we take into account both primary and secondary users' objectives. We use numerical methods in order to study how different parameters, such as assigned powers in the coding scheme, direct link reliability, and the number of secondary users affect the overall system performance. Our results show that the gain, which the primary user can achieve by cooperation, highly depends on the quality of its direct link as well as the secondary users' QoS requirements. Furthermore, the percentage of cooperation instances between secondary users and the primary user is dependent on the amount of power the secondary users allocate for relaying the primary's signal based on the direct link quality.
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| 7. |
- Tariq, Muhammad Assad, 1985, et al.
(författare)
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Performance of Circular QAM Constellations with Time Varying Phase Noise
- 2012
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Ingår i: IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC. - 9781467325691 ; , s. 2365-2370
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Konferensbidrag (refereegranskat)abstract
- Time varying phase noise is a limiting factor in high-speed wireless communication systems, e.g., microwave backhaul links in cellular networks. This paper seeks to investigate the performance of circular M-ary quadrature amplitude modulations (M-QAMs) in the presence of time varying phase noise. A new approximate union bound expression for the symbol-error probability (SEP) of a specific circular M-QAM constellation is derived. Numerical results show that this expression is accurate at medium-to-high signal-to-noise ratios (SNRs) for different constellation orders, M. Next, exact closed-form expressions for the SEP of binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) modulations in the presence of phase noise are derived. Extensive simulations are carried out to compare the performance of rectangular and circular QAM modulations in the presence of time varying phase noise, where it is demonstrated that circular QAM modulations can outperform their rectangular counterparts when considering the effect of time varying phase noise.
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| 8. |
- Yang, Jinghong, et al.
(författare)
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Robust receive beamforming with interference and channel uncertainty
- 2012
-
Ingår i: Personal Indoor and Mobile Radio Communications (PIMRC), 2012 IEEE 23rd International Symposium on. - : IEEE conference proceedings. - 9781467325691 ; , s. 2231-2236
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Konferensbidrag (refereegranskat)abstract
- In this paper, we introduce a general convex framework for robust beamforming, which is valid for both deterministic and stochastic uncertainty models, and provides robustness against errors both in the channel and in the interference co-variance matrix estimations. Furthermore, we extend our design to a multiple-state interference model and show the performance gains obtained by exploiting the interference structure.
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| 9. |
- Zheng, Gan, et al.
(författare)
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Multi-gateway cooperation in multibeam satellite systems
- 2012
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Ingår i: Personal Indoor and Mobile Radio Communications (PIMRC), 2012 IEEE 23rd International Symposium on. - : IEEE. - 9781467325691 ; , s. 1360-1364
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Konferensbidrag (refereegranskat)abstract
- Multibeam systems with hundreds of beams have been recently deployed in order to provide higher capacities by employing fractional frequency reuse. Furthermore, employing full frequency reuse and precoding over multiple beams has shown great throughput potential in literature. However, feeding all this data from a single gateway is not feasible based on the current frequency allocations. In this context, we investigate a range of scenarios involving beam clusters where each cluster is managed by a single gateway. More specifically, the following cases are considered for handling intercluster interference: a) conventional frequency colouring, b) joint processing within cluster, c) partial CSI sharing among clusters, d) partial CSI and data sharing among clusters. CSI sharing does not provide considerable performance gains with respect to b) but combined with data sharing offers roughly a 40% improvement over a) and a 15% over b).
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