Large Diversity Gain Research Articles

Even and odd mode CPW‐fed pattern diversity antenna for body centric communication systems

AbstractA patterns diversity slot antenna loaded with a dielectric resonator is presented for on‐body communication systems in 2.45 GHz band. The diversity is achieved by launching even and odd modes on coplanar feed lines resulting in end‐fire and broadside radiation pattern respectively. Loading of dielectric resonator enhances impedance bandwidth and improves isolation between broadside and end‐fire patterns. A common impedance bandwidth of 4% is obtained along with ports isolation of 22 dB. Diversity gain is calculated for three unique on‐body channels and the maximum diversity gain of 8.5 dB is achieved for nonline‐of‐sight on body channel. Large diversity gain and planar geometry makes this antenna suitable for various on‐body communication applications.

Diversity-Multiplexing Tradeoff of Dynamic Harvest-and-Forward Cooperation

We analyze the diversity-multiplexing tradeoff (DMT) of the dynamic harvest-and-forward (DHF) cooperation to clearly explain the achievable diversity order. Surprisingly, DHF cooperation with a relay that harvests energy from a wireless source achieves the same DMT as when the relay is connected to a fixed power supply, by supplying the energy harvesting (EH) period to be asymptotically small. For nontrivial EH period, however we show that the same DMT is achieved for a sufficiently small multiplexing gain (or corresponding large diversity gain), beyond which the DMT degrades.

Impact of the Channel State Information on the Energy-Efficiency of MIMO Communications

Although multiple-input multiple-output (MIMO) techniques provide attractive tools for reducing the energy consumption of wireless communications, many of them require transmitter-side channel state information (TCSI). While the effect of the TCSI on the MIMO channel capacity is well known, its impact on the achievable energy-efficiency is still not well determined. In this paper, we address this issue by studying the energy consumption of the singular value decomposition (SVD), beamforming, zero forcing and generalized Alamouti MIMO schemes. Although TCSI provides important savings in long-range communications, our results suggest that it is not critical when transmitting over short link distances. Results also show that large antenna arrays using schemes with a large diversity gain are energy-optimal for transmitting data over long transmission distances, while small arrays using schemes with a large multiplexing gain are more energy-efficient for performing short-range communications.

Space-Time-Coded Adaptive Spatial Modulation in Wireless MIMO Communication Systems

AbstractIn this paper, we consider a wireless multi-antenna system using a promising technique, i.e., spatial modulation, and propose an adaptive spatial modulation (ASM) scheme embedded Alamouti space-time block coding (STBC). Instead of selecting one active antenna in each transmission in conventional ASM, we activate two antennas as one antenna group simultaneously to encode the information bits into Alamouti code blocks, each of which needs two channels used. Two detection schemes are presented in different channel conditions, i.e., the maximum likelihood (ML) detection and an adaptive modulation-order selection algorithm. Simulation results show that the proposed scheme improves the error performance and provides larger diversity gain compared to conventional spatial modulation and adaptive spatial modulation.

Outage-Optimal TDMA Based Scheduling in Relay-Assisted MIMO Cellular Networks

In multi-access wireless networks, transmission scheduling is a key component that determines the efficiency and fairness of wireless spectrum allocation. At one extreme, greedy opportunistic scheduling that allocates airtime to the user with the largest instantaneous channel gain achieves the optimal spectrum efficiency and transmission reliability but the poorest user-level fairness. At the other extreme, fixed TDMA scheduling achieves the fairest airtime allocation but the lowest spectrum efficiency and transmission reliability. To balance the two competing objectives, extensive research efforts have been spent on designing opportunistic scheduling schemes to reach certain tradeoff points between the two extremes by tuning the greediness in scheduling policy. In this paper and in contrast to the conventional wisdom, we find that in relay-assisted MIMO cellular networks, being greedy in user scheduling is unnecessary since it does not directly translate to larger diversity gain. When each mobile user has no less antennas than the base station, even fixed TDMA achieves the optimal diversity gain that is otherwise achievable by greedy opportunistic scheduling. In addition, by incorporating very limited opportunism, a simple TDMA-based scheme, named relaxed-TDMA, asymptotically achieves the same optimal system reliability in terms of outage probability as greedy opportunistic scheduling. This reveals a surprising fact: transmission reliability and user fairness are not necessarily contradicting each other in relay-assisted systems. They can be both achieved by the simple TDMA schemes. For practical implementations, we further propose a fully distributed algorithm to implement the relaxed-TDMA scheme. Our results here may find applications in the design of next-generation wireless communication systems with relay architectures such as LTE-advanced and WiMAX.

A SELECTIVE LINEAR TRANSCEIVER DESIGN OVER CORRELATED LARGE-MIMO CHANNELS

With tens or an even larger number of antennas utilized, large-MIMO systems have many potential merits. However, there are also some di-culties with its practical realization. For example, the feedback overhead caused by sending back a large precoding matrix is heavy. In this paper, we propose a selective linear transceiver scheme to reduce the overwhelming feedback overhead in correlated large-MIMO systems. In line with the required reduced amount of feedback, antennas which can provide a potentially large diversity gain are flrstly chosen independently of the actual channel realization. The transceiver is then designed over correlated MIMO channels in an iterative way to minimize the sum of detection errors under the transmit power constraint. Although optimal solutions for the case of full transceiver have been given under some special scenarios, we modify them to improve the BER performance of systems. Monte- Carlo simulation results verify that the proposed selective linear transceiver is a useful scheme in large-MIMO systems to provide a tradeofi between performance and feedback overhead.

Green Wireless Communications: A Time-Reversal Paradigm

Green wireless communications have received considerable attention recently in hope of finding novel solutions to improve energy efficiency for the ubiquity of wireless applications. In this paper, we argue and show that the time-reversal (TR) signal transmission is an ideal paradigm for green wireless communications because of its inherent nature to fully harvest energy from the surrounding environment by exploiting the multi-path propagation to re-collect all the signal energy that would have otherwise been lost in most existing communication paradigms. A green wireless technology must ensure low energy consumption and low radio pollution to others than the intended user. In this paper, we show through theoretical analysis, numerical simulations and experiment measurements that the TR wireless communications, compared to the conventional direct transmission using a Rake receiver, reveals significant transmission power reduction, achieves high interference alleviation ratio, and exhibits large multi-path diversity gain. As such it is an ideal paradigm for the development of green wireless systems. The theoretical analysis and numerical simulations show an order of magnitude improvement in terms of transmit power reduction and interference alleviation. Experimental measurements in a typical indoor environment also demonstrate that the transmit power with TR based transmission can be as low as 20% of that without TR, and the average radio interference (thus radio pollution) even in a nearby area can be up to 6dB lower. A strong time correlation is found to be maintained in the multi-path channel even when the environment is varying, which indicates high bandwidth efficiency can be achieved in TR radio communications.

Rate Allocation for Cooperative Orthogonal-Division Channels with Dirty-Paper Coding

This paper investigates how much the rate region of the two-user Gaussian interference channel can be enlarged by allowing the two source nodes to cooperate. Two cooperative transmission schemes are proposed, based on dirty-paper coding and the assumption that the radio bandwidth is partitioned into two parts, and each part is utilized by one source node. The achievable rate regions and the outage performance of these two schemes are compared with the simplified Han-Kobayashi scheme, which is an efficient coding scheme for the interference channel. Simulation results show that in some channel realizations, the rate region of the Han-Kobayashi scheme is a subset of the rate regions of our two proposed cooperative transmission schemes. Furthermore, a significant gain in outage performance can be obtained, as the cooperative schemes have twice the diversity order of the simplified Han-Kobayashi scheme. While both cooperative schemes are able to yield large diversity gain, one of them can be implemented by simple decoder. Besides, it has an efficient algorithm for maximizing its weighted sum rate, and can be extended easily to the multi-channel case.

Phase ambiguity diminishing space-time trellis codes

Phase ambiguities affect any joint decoding and channel estimation algorithm over fading channels, making codes that mitigate this problem of considerable interest. This work presents a design that transforms a Space-Time Trellis Code (STTC), prone to carrier phase ambiguities, into a Phase Ambiguity Diminishing STTC (PAD-STTC) that is robust to such impairment. A PAD-STTC can be considered as a Multiple STTC (MSTTC) with special constellation mappings. The design criteria for these mappings are developed in this work by trading among the PAD property, diversity, and coding gain. Two PAD-STTC structures termed PAD1-STTC and PAD2-STTC are proposed, where PAD2-STTC increases the number of states over the constituent STTC. Computer simulation results indicate that PAD-STTCs can solve the phase ambiguity problem and provide a larger diversity gain than the constituent STTC over high Doppler fading channels. Moreover, with the same constituent STTC, the PAD2-STTC outperforms the PAD1-STTC at the expense of increased complexity.

Diversity Gains of Power Control With Noisy CSIT in MIMO Channels

A multi antenna channel with partial channel state information at the transmitter (CSIT) is studied. The partial CSIT takes the form of the channel matrix corrupted by additive white Gaussian noise (AWGN) with a variance that is assumed to decay as a power of the signal-to-noise ratio (SNR). It is shown that under a long-term power constraint and in the regime of asymptotically high SNR, a large diversity gain over the channel can be achieved by using rarely a high power at the transmitter that compensates for bad channel realizations. Examples relating the diversity gain of the systems with the channel Doppler bandwidth are discussed.

Performance Comparison between CDTD and STTD for DS-CDMA/MMSE-FDE with Frequency-Domain ICI Cancellation

SUMMARY Frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion can provide a better bit error rate (BER) performance than rake combining. However, the residual inter-chip interference (ICI) is produced after MMSE-FDE and this degrades the BER performance. Recently, we showed that frequency-domain ICI cancellation can bring the BER performance close to the theoretical lower bound. To further improve the BER performance, transmit antenna diversity technique is effective. Cyclic delay transmit diversity (CDTD) can increase the number of equivalent paths and hence achieve a large frequency diversity gain. Space-time transmit diversity (STTD) can obtain antenna diversity gain due to the space-time coding and achieve a better BER performance than CDTD. Objective of this paper is to show that the BER performance degradation of CDTD is mainly due to the residual ICI and that the introduction of ICI cancellation gives almost the same BER performance as STTD. This study provides a very important result that CDTD has a great advantage of providing a higher throughput than STTD. This is confirmed by computer simulation. The computer simulation results show that CDTD can achieve higher throughput than STTD when ICI cancellation is introduced.

Single-Carrier Based Multiplexing of Layer 1/Layer 2 Control Signals in Evolved UTRA Uplink Using DFT-Spread OFDM

This paper proposes efficient single-carrier (SC) based multiplexing schemes for Layer 1 (L1)/Layer 2 (L2) control signals in SC-FDMA radio access using DFT-Spread OFDM in the Evolved UTRA uplink. L1/L2 control signals are necessary for key packet access techniques such as downlink scheduling, link adaptation, hybrid automatic repeat request (ARQ) with soft combining, and for uplink feedback control signals. We first propose a SC-based multiplexing scheme for L1/L2 control signals within a shared data channel for a set of user equipment (UE) that transmits both an uplink shared data channel and L1/L2 control signals within the same subframe. We also propose a multiplexing scheme for L1/L2 control signals without uplink data transmission that takes advantage of intra-subframe frequency hopping (FH) using multiple exclusively-assigned time-frequency resource blocks (RBs) to obtain a frequency diversity gain. Furthermore, we propose an orthogonal CDMA-based multiplexing scheme using cyclic shifts of a constant amplitude zero auto-correlation (CAZAC) sequence for L1/L2 control signals from different UEs within the same narrowband time-frequency RB. Computer simulation results show that the proposed SC-based multiplexing scheme for the L1/L2 control signals within the shared data channel achieves a higher user throughput than a multicarrier-based multiplexing scheme. The results also show that the proposed multiplexing scheme for the L1/L2 control signals that takes advantage of the intra-subframe FH for the UE without uplink data transmission achieves high quality reception through large frequency diversity gain. Furthermore, we show that the proposed cyclic-shift based orthogonal CDMA multiplexing is effective in the multiplexing of multiple L1/L2 control signals from different UEs within the same RB.

On the Study of Network Coded AF Transmission Protocol for Wireless Multiple Access Channels

In this correspondence, the performance of the network coded amplify-forward cooperative protocol is studied. The use of network coding can suppress the bandwidth resource consumed by relay transmission, and hence increase the spectral efficiency of cooperative diversity. A distributed strategy of relay selection is applied to the cooperative scheme, which can reduce system overhead and also facilitate the development of the explicit expressions of information metrics, such as outage probability and ergodic capacity. Both analytical and numerical results demonstrate that the proposed protocol can achieve large ergodic capacity and full diversity gain simultaneously.

Asynchronous cooperative transmission mechanism using distributed Orthogonal Frequency Division Multiplexing for mobile ad hoc networks

In this article, we propose an asynchronous cooperative transmission mechanism for Mobile ad hoc Networks (MANETs). The proposed cooperative transmission mechanism employs distributed Unitary Space-Frequency Coded-Orthogonal Frequency Division Multiplexing (USFC-OFDM), which does not require any channel estimation and has a lower decoding complexity, and therefore can provide better reliability and robustness when mobile nodes move fast. Moreover, it can achieve a larger diversity gain and multiplexing gain, and can thus combat fast time-varying and frequency-selective channel fading, and tolerate imperfect synchronisation among mobile nodes. To support USFC-OFDM, a Time Division Multiple Access-based Cooperative Medium Access Control protocol and an on-demand Cooperative Dynamic Source Routing protocol are also proposed. Through simulation results, we show that the proposed USFC-OFDM-based cooperative transmission mechanism can significantly improve the network performance in terms of packet delivery ratio and bit error rate in highly dynamic mobile environments.

Diversity gain measurements of a reconfigurable antenna with switchable polarization

AbstractThis article presents an experimental investigation on the diversity performance of a reconfigurable antenna integrating a SPDT for polarization switching. The antenna is characterized in terms of its envelope correlation factor, mean effective gain, and diversity gain (DG) in a multipath indoor environment. The influence of the antenna placement and orientation is emphasized. Low correlation factors and large DGs are observed making this device highly performing for indoor wireless communication systems. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 3154–3158, 2007; Published online in Wiley Inter‐Science (www.interscience.wiley.com). DOI 10.1002/mop.22904

TPC-based STBC multiuser detection with LSE-RLS algorithm

The Bit Error Rate (BER) performance of a Turbo Product Code (TPC) based Space-Time Block Coding (STBC) multiuser wireless system in the frequency-selective channels has been investigated. Both of the good error correcting capability of TPC and the large diversity gain of STBC can be achieved simultaneously. A Least Square Error-Recursive Least Square (LSE-RLS) algorithm is applied to estimate the channel and cancel the interference. Simulations show that the proposed system can obtain about 2.7dB gain in E s /N 0 at the BER of 10−3.

System Performance of Concatenated STBC and Block Turbo Codes in Dispersive Fading Channels

A new scheme of concatenating the block turbo code (BTC) with the space-time block code (STBC) for an OFDM system in dispersive fading channels is investigated in this paper. The good error correcting capability of BTC and the large diversity gain characteristics of STBC can be achieved simultaneously. The resulting receiver outperforms the iterative convolutional Turbo receiver with maximuma posteriori probability expectation-maximization (MAP-EM) algorithm. Because of its ability to perform the encoding and decoding processes in parallel, the proposed system is easy to implement in real time.

Comparison of Throughput Employing Hybrid ARQ Packet Combining in Forward Link OFCDM Broadband Packet Wireless Access

This paper compares the throughput performance employing hybrid automatic repeat request (ARQ) packet combining, i.e., Chase combining, and Incremental redundancy, considering the frequency diversity effect in the broadband forward-link channel for Orthogonal Frequency and Code Division Multiplexing (OFCDM) packet wireless access achieving a peak throughput above lOOMbps. Simulation results show that the achievable throughput at the average received signal energy per symbol-to-background noise power spectrum density ratio (E s /N 0 ) of 0 and 6 dB employing Incremental redundancy is increased by approximately 35 and 30% compared to that using Chase combining for QPSK and 16QAM data modulation schemes with the coding rate of R = 1/2, respectively, considering a large frequency diversity effect in a 12-path exponential decayed Rayleigh fading channel, since the reduced variations in the received signal level in a broadband channel bring about a larger coding gain in Incremental redundancy. We also show that when adaptive modulation and channel coding (AMC) is applied, Incremental redundancy is superior to Chase combining since the large coding gain is effective in achieving a large time diversity gain for a low number of retransmissions such as M = 1 or 2 for a maximum Doppler frequency up to f D = 400 Hz. It is demonstrated, nevertheless, that the total throughput when employing Incremental redundancy associated with a near optimum MCS set according to the channel conditions becomes almost identical to that using Chase combining when a large number of retransmissions, M, is allowed, such as M = 10, owing to time diversity alone with frequency diversity.

Enhanced Space-Time Block Coded Systems by Concatenating Turbo Product Codes

The BER performance of a turbo product code (TPC) based space-time block coding (STBC) wireless system has been investigated. With the proposed system, both the good error correcting capability of TPC and the concurrent large diversity gain characteristic of STBC can be achieved. The BER upper bound has been derived taking BPSK modulation as an example. The simulation results show that the proposed system with the concatenated codes outperforms the one with only TPC or STBC and other reported schemes that concatenate STBC with convolutional Turbo codes or trellis codes.

Simultaneous wide-band four-antenna wireless channel-sounding measurements at 1920 MHz in a suburban environment

Simultaneous four-antenna wide-band mobile channel-sounding measurements were made in two areas at 1920 MHz. The received signal strength and transmission loss were examined. Path-loss exponents for the two sectors were found to be 4.9 and 4.1. Root mean square delay spreads for the two sectors were found to be less than 1.38 and 0.65 /spl mu/s for 90% of the data and less than 3.14 and 1.35 /spl mu/s for 99% of the data. Fast fading reduction using antenna diversity and increased channel bandwidth (19.6 kHz, 1.25 MHz, 5.0 MHz, and 10.0 MHz) were examined. Three signal combining methods were considered: selection diversity, equal gain combining, and maximal ratio combining. The measured results show that increasing the number of diversity antennas or the channel bandwidth significantly reduces fading. Maximal ratio combining yields the largest diversity gain, exceeding 11.0 and 17.0 dB at the 90% and 99% fast fade depth probability levels, respectively, for the 19.6-kHz narrow-band signal and 6.7 and 6.9 dB for the 10.0-MHz broad-band signal when all four channels are used.