Ersin Sengul

A MIMO System With Multifunctional Reconfigurable Antennas

A multiple-input-multiple-output (MIMO) system equipped with a new class of antenna arrays, henceforth referred to as multifunction reconfigurable antenna arrays (MRAAs), is investigated. The elements of MRAA, i.e., multifunction reconfigurable antennas (MRAs) presented in this work are capable of dynamically changing the sense of polarization of the radiated field thereby providing two reconfigurable modes of operation, i.e., polarization diversity and space diversity. The transmission signaling scheme can also be switched between transmit diversity (TD) and spatial multiplexing (SM). The results show that the reconfigurable modes of operation of an MRAA used in conjunction with adaptive space-time modulation techniques provide additional degrees of freedom to the current adaptive MIMO systems, resulting in more robust system in terms of quality, capacity and reliability. A performance gain up to 30 dB is possible with the proposed system over conventional fixed antenna MIMO systems depending on the channel conditions

Bit Interleaved Coded Multiple Beamforming

In this paper, we investigate the performance of bit-interleaved coded multiple beamforming (BICMB). We provide interleaver design criteria such that BICMB achieves full spatial multiplexing of min( N, M) and full spatial diversity of NM with N transmit and M receive antennas over quasi-static Rayleigh flat fading channels. If the channel is frequency selective, then BICMB is combined with orthogonal frequency division multiplexing (OFDM) (BICMB-OFDM) in order to combat ISI caused by the frequency-selective channels. BICMB-OFDM achieves full spatial multiplexing of min(N, M), while maintaining full spatial and frequency diversity of NML for an NtimesM system over L-tap frequency-selective channels when an appropriate convolutional code is used. Both systems analyzed in this paper assume perfect channel state information both at the transmitter and the receiver. Simulation results show that, when the perfect channel state information assumption is satisfied, BICMB and BICMB-OFDM provide substantial performance or complexity gains when compared to other spatial multiplexing and diversity systems.

Diversity analysis of single and multiple beamforming

Multi-antenna communication systems have the potential to play an important role in the design of the next generation broadband wireless communication systems. In this paper, we study a single-user multi-antenna system with perfect channel state information (CSI) both at the transmitter and the receiver. Beamforming is used to exploit the perfect channel knowledge at both ends. We show that beamforming achieves the maximum diversity in space when only the best eigenmode is used (i.e., single beamforming). We extend our analytical results to multiple beamforming (i.e., sending more than one symbol simultaneously). Our main contribution is the analysis of the maximum achievable diversity order of beamforming systems.

Performance analysis of beamforming for MIMO OFDM with BICM

In this paper we show and quantify both analytically and via simulations that the use of channel knowledge at the transmitter, the technique known as beamforming, achieves the maximum diversity in space when the best eigenmode is used (single beamforming). Furthermore, we investigate beamforming in conjunction with next generation wireless local area networks (WLAN). It is known that the widely used technique in WLAN, bit interleaved coded modulation (BICM) with orthogonal frequency division multiplexing (OFDM), can achieve the maximum frequency diversity order that is inherited in the channel. We show that the combination of BICM, single beamforming, and OFDM also leads to the maximum diversity order in space and frequency domains. In other words, for systems with N transmit and M receive antennas, BICM beamforming-OFDM (BBO) can achieve a diversity order of NML over L-tap frequency selective channels by using an appropriate convolutional code. In addition to having a substantial diversity order, simulation results show that beamforming and BBO introduce significant coding gains when compared to other systems based on space time block codes (STBC) with the same diversity order.

Bit-Interleaved Coded Multiple Beamforming with Imperfect CSIT

This paper addresses the performance of bit-interleaved coded multiple beamforming (BICMB) [1], [2] with imperfect knowledge of beamforming vectors. Most studies for limited-rate channel state information at the transmitter (CSIT) assume that the precoding matrix has an invariance property under an arbitrary unitary transform. In BICMB, this property does not hold. On the other hand, the optimum precoder and detector for BICMB are invariant under a diagonal unitary transform. In order to design a limited-rate CSIT system for BICMB, we propose a new distortion measure optimum under this invariance. Based on this new distortion measure, we introduce a new set of centroids and employ the generalized Lloyd algorithm for codebook design. We provide simulation results demonstrating the performance improvement achieved with the proposed distortion measure and the codebook design for various receivers with linear detectors.We show that although these receivers have the same performance for perfect CSIT, their performance varies under imperfect CSIT.

Achieving full spatial multiplexing and full diversity in wireless communications

It is well-known that using multiple antennas provides a substantial capacity and diversity increase for wireless communication systems. A multi-input multi-output (MIMO) technique that utilizes the channel knowledge both at the transmitter and the receiver is known as beamforming. Beamforming separates a MIMO channel into parallel subchannels. It was previously shown that uncoded beamforming achieves a diversity order of (N - S + 1)(M - S + 1) if S symbols are transmitted simultaneously for N transmit and M receive antennas. Hence, there is a significant drop in the diversity order (and performance) of the system with increased spatial multiplexing. In this paper, we introduce bit interleaved coded multiple beamforming and name the system BICMB. We provide interleaver design criteria such that the resulting system achieves full spatial multiplexing of min(N, M) and full spatial diversity of NM. Simulation results show that BICMB, due to its ability of maintaining the maximum diversity order even at full spatial multiplexing, provides substantial performance gain when compared to the best spatial multiplexing systems

MIMO BICM-OFDM Beamforming with Full and Partial CSIT

In this paper we analyze single beamforming in combination with bit interleaved coded modulation (BICM) and OFDM. We show that BICM-beamforming-OFDM (BBO) achieves full diversity in space and frequency independent of the power delay profile of the channel. Since only one stream of data is transmitted over all transmit antennas, a simple interleaver is shown to be sufficient to achieve full space and frequency diversity. Simulation results show that beamforming-based systems introduce substantial coding gain, even with partial channel state information at the transmitter (CSIT), when compared to other systems based on space time block codes (STBC) with the same full diversity order.

A MIMO system equipped with multifunctional reconfigurable antennas

A MIMO system equipped with a new class of antenna arrays, henceforth referred to as multifunction reconfigurable antenna arrays (MRAAs), is investigated. The elements of MRAA, i.e. MRAs presented in this work are capable of dynamically changing the sense of polarization of the radiated field thereby providing two reconfigurable modes of operation, i.e. polarization diversity and space diversity. The transmission signaling scheme can also be switched between transmit diversity (TD) and spatial multiplexing (SM). The results show that the reconfigurable modes of operation of an MRAA used in conjunction with adaptive space-time modulation techniques provide additional degree of freedoms to the current adaptive MIMO systems, thereby resulting in more robust system in terms of quality, capacity and reliability. A substantial performance gain is achievable with the proposed system over conventional fixed antenna MIMO systems depending on the channel conditions

A spectrally efficient PMR system utilizing broadcast service

Different trunked Private Mobile Radio (PMR) systems have been designed over the last several decades, all of which have symmetric downlink and uplink channel capacities. Due to this symmetry, these systems may not be spectrally efficient in case of different types of services, which are specific to PMR systems, such as group and broadcast calls. In this study, a new asymmetric trunked PMR system comprising a broadband, wide-area downlink and a narrowband cellular uplink, is proposed to achieve a higher spectral efficiency than current digital trunked PMR systems. This system is spectrally more efficient because in group and broadcast calls only a single downlink channel has to be allocated in the downlink part. However, as the number of clusters in the system increases, this advantage relative to PMR systems is lost, since the latter can employ frequency reuse. Spectral efficiency of the proposed asymmetric system (a-PMR) system and a standard TETRA system are compared using numerical case studies against different traffic loads and number of clusters. The optimum point, with respect to number of clusters, up to which the proposed a-PMR system is more efficient, is determined. It is shown that a very large PMR user population can be efficiently served using the proposed a-PMR system. The issues related to implementing such a system are discussed.

Adaptive Modulation and Coding for Bit Interleaved Coded Multiple Beamforming

Bit interleaved coded multiple beamforming (BICMB) was previously designed to achieve full spatial multiplexing of min(N, M) and full spatial diversity of NM for N transmit and M receive antennas over flat fading channels. Furthermore, BICMB when combined with orthogonal frequency division multiplexing (OFDM) achieves full spatial multiplexing and full diversity order of NML over L-tap frequency-selective channels. BICMB requires full channel state information (CSI) both at the transmitter and receiver, however it uses uniform power and rate over the parallel channels established by multiple beamforming. In this paper, our main goal is to investigate the performance of the previously analyzed BICMB system via adaptive modulation and coding (AMC) to further utilize CSI and to improve system throughput performance. Hence, we name the new systems as adaptive BICMB (ABICMB) over flat fading, and ABICMB-OFDM over frequency-selective channels. Simulation results show that adaptive system achieves 4-13 dB performance gain compared to non-adaptive case depending on the antenna configuration and environment. Systems analyzed require perfect CSI both at the transmitter and receiver, which may be difficult to obtain in a practical scenario. However, high performance gains achieved makes it worthwhile to study the performance of the proposed systems, leaving room for significant gain with limited feedback