Space Time Block Code

ABSTRACT: Wireless communication is a popular method used worldwide for data transmission and reception. For larger capacity and higher data rate we use MIMO system. MIMO-OFDM combines multiple input, multiple output (MIMO) technology and orthogonal frequency division multiplexing (OFDM). This work provides an overview of Space-Time Block Code (STBC)-OFDM system and Space-Frequency Block Code (SFBC)-OFDM and a comparison between them are introduced.

The design of wireless systems is open for further improvements in respect of spectrum efficiency, coverage area and link reliability. Multiple-Input-Multiple-Output (MIMO) links are capable to overcome the limitations of data rate and range of wireless devices by exploiting bandwidth efficiency of multiple transmit and receive antennas. Improved efficiency can further be possible by incorporating the Space Time Block Code (STBC) with MIMO system. Researches on MIMO systems with STBC have becoming an important area that improves the performance of system without additional bandwidth or transmit power requirements. This paper presents STBC models in Ricean fading environment using various combinations of transmit and receive antenna numbers. The simulations results have been obtained in MATLAB platform. The bit error rate performance has been analyzed for the Ricean factors of k = 0, 1, and 10 in both the BPSK and 16 QAM modulation schemes.

Decoding is performed at the receiver side. For linear processing of signals maximum likelihood decoding is employed in space time block code. In case of space time block code , if there are 2 b signals in the constellation ,then at time slot one 2b bits arrive at the encoder and select two complex symbols and . The symbols and are simultaneously transmitted from antenna one and two respectively.

More recently, space-time block codes (STBC) based differential space-time block code (DSTBC) modulation scheme was proposed in [10]. DSTBC has the same diver- sity gain as but offers higher coding gain than the unitary group code based DSTM schemes. This is not surprising in view of the fact that STBC is optimal in terms of SNR [11]. Moreover, the decoding of the DSTBC modulation scheme is more efficient than for the DSTM schemes, especially for large constellations, since the former allows for a decoupled linear detection, with which it is to detect each information symbol separately.

Abstract—In the recent years, extensive studies have been done to design space-time codes appropriate for communications over fading channels in multiple input-multiple output (MIMO)systems. Most of these designs have been based upon the assumption that the channel fading coefficients are uncorrelated hence independent jointly Gaussian random variables. Naturally the best strategy in such situations that the elements of the channel matrix are independent is to employ diversity techniques to combat the adverse effects of these fading media and thus the most famous space-time codes, i.e., orthogonal and trellis codes have been designed with an eye to realizing the maximum attainable diversity order in a MIMO system. In this paper, we will remove this almost ever-present yet practically difficult to meet condition and shall introduce a new linear space-time block code that due to having some inherent redundancy as well as diversity is well- suited to correlated fading channels. We will discuss the properties of the proposed code, derive its maximum likelihood (ML)decoder and provide simulation results which show its superiority to the highly used orthogonal space-time block codes in a wide range of signal to noise ratios in correlated fading channels.

Abstract: This paper presents the average capacity and error performance of 3×4 orthogonal space time block code (OSTBC) and transmits antenna selection (TAS) with multiple antennas. In TAS scheme, we consider one transmit antenna is selected for transmit signals at the secondary transmitters and the secondary receiver applies the maximum likelihood (ML). In 3×4 OSTBC scheme, we consider three transmit antennas and four receive antennas. The experimental results shown that the average capacity and bit error rates are better performance of 3×4 OSTBC is comparing to TAS scheme. We propose a codebook design and feedback scheme that combines space-time block coding and array processing. To the best of our knowledge, this is the first scheme with quantized feedback that can achieve low-complexity de-coding and full diversity for any number of users when all users transmit

The growth in high data rate mobile data transmission in recent years is due to the tremendous achievements in Digital Communication especially Digital Modulation Techniques starting from Second Generation system (2G) in early 80’s to today 4G (LTE – Advanced). To achieve the goal towards Shannon’s Channel Capacity, a no. of modulation techniques are developed during these years. With the tremendous growth in the Very Large Scale Integrated Circuits (VLSI), a no. of digital modulation techniques is easier to implement in convenient manner. Orthogonal Frequency Division Multiplexing (OFDM), one of the latest techniques became feasible and economical due to the high processing speed. OFDM in combination with other techniques like Space Time Block Code (STBC)Phase shift key (PSK) and Quadrature Amplitude Modulation (QAM) give better performances in case of Multi- input Multi-output System (MIMO).

In the first time slot, the source serially transmits two data blocks to two relays. In the next time slot, one relay only amplifies and forwards its received signals, while the other precodes its received data blocks by a precoding matrix before transmitting to the destination as illustrated in Figure 1. The idea behind our design is that precoding in R 2 is designed to send the second column of the block

Orthogonal Frequency Division Multiplexing (OFDM) is a system in which the aggregate transmission data transfer capacity is part into various orthogonal subcarriers with the goal that a wideband flag is changed in a parallel game plan of narrowband „orthogonal‟ signals. Thusly, a high information rate stream that would some way or another require a channel data transmission a long ways past the real intelligence transfer speed can be isolated into various lower rate streams. Expanding the quantity of subcarriers builds the image time frame so that, in a perfect world, a recurrence specific blurring channel is transformed into a level blurring one. As it were, OFDM handles recurrence particular blurring coming about because of time scattering of multipath channels by growing the image length [1].

The Three Generation Partnership Project (3GPP) started the next generation wireless systems (4G) under the project Long Term Evolution Advanced (LTE-A) in 2008 [5]. In LTE-A, user equipment (UE) is imposed two transmit antennas. Therefore, STBC scheme can be the most popular candidate for the uplink diversity gain [6]. Alamouti STBC scheme sounds a suitable candidate in LTE-A systems. Unfortunately, in LTE frame structure is dedicated 3-time slots with Alamouti STBC scheme. This has brought up an interesting STBC design problem which is compatible with LTE frame structure. Hybrid STBC scheme as the first scheme has been proposed for 3-time slots and two transmit antennas systems [7]. Its encoding matrix includes two time slots Alamouti scheme followed by one time slot repetition transmission. Although, the Hybrid scheme achieves code rate one and its decoding complexity is linear at receiver does not achieve full diversity. To remove full diversity defect, a class of QSTBC scheme is proposed by Lie et al. in [8] [9]. The QSTBC scheme achieves code rate one and full diversity. But, there are two problems with this scheme. The first problem is highcomplexity of maximum likelihood (ML) decoding which requires a joint detection of two complex symbols (O(M 2 )), where M is size of the used symbol constellation. The second problem is that the minimum determinant values (MDVs) extremely vanish by increasing the symbol constellation size. Recently, Fast-Group-Decodable STBC (Fast-GSTBC) scheme has been proposed in [10] [11]. As generic construction method for odd-time slot, new GSTBC scheme has been designed for LTE-A that achieves code rate one and full diversity with symbol-wise decoding com- plexity (O(M 1 )) [12]. GSTBC scheme achieves code rate one and full diversity with symbol-wise decoding complexity (O(M 1 )). However, GSTBC scheme reduces decoding complexity for 3-time slots two transmit an- tennas its MVDs vanish. Also, this scheme is not compatible with single antenna.

Blind recognition of space-time block codes (STBCs) used in multiple transmitter communication is an important research topic in the non-cooperative scenario, which has attracted more and more attention recently. However, all of the current recognition algorithms can only work well in multiple-input multiple-output system, i.e., the system employs multiple receive antennas. To our knowledge, there is no report in the literature on blind recognition of STBCs in multiple-input single-output (MISO) system, i.e., the system employs only one receive antenna. In this paper, this matter is addressed. An original method of feature extraction for STBCs in the MISO system is proposed using the second-order and higher-order statistics of the reconstructed receiver. After feature extraction, the classification of space-time code can be considered as a pattern recognition problem. A classifier based on a support vector machine is proposed for the recognition of STBCs by mapping these features into a high dimensional space. Simulations show that the proposed classifier can recognize STBCs with high performance and be robust to modulation.

Abstract - Now-a-days a speedy and more reliable communication links along with Multiple-input-multiple-output (MIMO) systems has become a prime concern in the field of Communication systems. As MIMO systems utilizes multiple number of antennas both at the transmitter and receiver, the necessary requirement to reduce the fading resulting from signal fluctuations in the channel is Diversity. In this paper the analysis of MIMO systems using STBC codes and OSTBC codes and measured the BER vs. Eb/N0 values have been carried out. The performance analysis of space–time block-coded multiple-input–multiple-output (STBC-MIMO) systems in different fading channels such as Rayleigh channel and Additive White Gaussian Channel (AWGN) channel is presented in this paper. Comparative analysis of average bit error rate (BER) of STBC-MIMO for binary phase-shift keying (BPSK), quadrature phase shift keying (QPSK) and Quadrature amplitude modulation (QAM) – both 8-QAM and 16-QAM are derived. Based on asymptotic analysis for both these fading channels, closed-form expressions of approximate average BER is obtained for different Eb/N0.

To elaborate a little further, from Figure 4 and 5 we surmise that fixed modulation schemes might become more attractive, when the diversity order increases, which is achieved in this case by employing more receivers. This is because for a certain average channel SNR, the probability of a particular modulation mode in- creases. In other words, the fading channel has become an AWGN- like channel, as the diversity order is increased. In Figure 6 we show our throughput performance comparison between AOFDM and fixed modulation based OFDM in conjunction with the space- time block code G 2 employing (a) one receiver and (b) two re-

Wireless access networks like WiMAX provide an excellent opportunity for operators to participate in the rapid growth opportunities that exist in emerging markets. The mobile Worldwide Interoperability for Microwave Access (WiMAX) is based on IEEE 802.16 standard and is used for wireless Metropolitan Area Network (MAN). The inclusion of Multiple Input Multiple Output (MIMO) in mobile WiMAX system provides a robust platform for space, time and frequency selective fading conditions and increases both data rate and system performance.The performance of mobile MIMO WiMAX system has been carried out using Space Time Block Code for different modulation schemes under different channel conditions like AWGN, Rayleigh channels etc. The result are encouraging because with respect to other services the WiMax getting better responses in term of WiMAX’s users and operators. The simulation of MIMO-mobile WiMAX model is done by using MATLAB

(STBC) for high-speed communications over power line channels (PLC) affected by quasi-static flat Rayleigh fading and additive man-made asynchronous impulsive noise is presented. Although the diversity order is severely reduced in a 3-phase PLC environment with respect to wireless MIMO channels, our simulation results for a rate-1 real orthogonal STBC scheme demonstrate significant gains over an uncoded system operating with the same diversity advantage. In addition, taking advantage of the spatial orthogonality provided by the power line channel, a rate-3/2 real non-orthogonal space-time block code with reduced diversity order is constructed. It is shown that using the proposed high-rate code in a power line communication system yields good performance with very high spectral efficiency.

The primary purpose of this paper is to present the space time block code for wireless networks that uses multiple numbers of antennas at both transmitter and receiver. LTE aims to provide enhanced service quality over 3G systems in terms of throughput, spectral efficiency, latency, peak data rate, and the MIMO techniques. Among several operational modes of MIMO, MU-MIMO, the base station transmits multiple streams to multiple users, has received much attention as a way of achieving improvement in performance. Space time wireless technology uses, multiple antennas along with appropriate signaling and receiver techniques offer a powerful tool for improving wireless performance. Space time block coding has been trying to incorporate in the fourth generation of mobile communications, which aims to deliver true multimedia capability. Simulation results have been shown that the STBC which includes the alamouti scheme as well as an orthogonal STBC for 4, 8 transmit antenna case has been simulated and studied. With orthogonal STBC, we have developed an 8 array antenna, which effectively handles large amount of data during transmission.

A multiple-input multiple-output (MIMO) communication system has an increased spectral efficiency in a wireless channel. It can provide both high rate transmission and spatial diversity between any transmit-receive pair. The appropriate space time block code (STBC) allows us to achieve, or approach, channel capacity for the flat fad- ing propagation channel with multiple antennas [1–4]. Moreover, an orthogonal frequency division multiplexing (OFDM) system transforms a frequency selective fading channel into a number of parallel subsystems with flat fading. It can eliminate the inter symbol interference (ISI) completely by inserting a long enough cyclic prefix (CP). The MIMO-OFDM system has attracted much attention for future broadband wireless systems and has already been implemented in IEEE802.11n, WiMax [5] and 3G-LTE systems [6, 7].

Space-time block codes (STBCs) are used for reliable high rate transmission over wireless digital channels with multiple antennas at both the transmitter and receiver ends. From the mathematical point of view, a space-time block code is a set of complex n × m matrices, the codebook, that satisfies a number of properties which determine how well the code performs. Recently, several different constructions of nonassociative algebras appeared in the liter- ature on fast decodable STBCs, cf. for instance Markin and Oggier [1], Srinath and Rajan [2], or [4], [5], [8], [9]. There are two different types of algebras involved. The aim of this paper is to present them in a unified manner and investigate their structure, in order to be able to build the associated (fully diverse, fast-decodable) codes more efficiently in the future.

The study of wireless communications with multiple transmit and receive antennas has been conducted expansively in the literature on information theory and communications. It has been known from the information-theoretic results that the application of multiple antennas in wireless systems can significantly improve the channel capacity over the single-antenna systems with the same requirements of power and bandwidth. Receive diversity existed as far back as 1960 [1]. However, receive diversity is not suitable for downlink in mobile communications, hence transmit diversity has attracted attention. Alamouti presented basic two transmit diversity scheme [2] which has remarkably low decoding complexity. Tarokh et al. [3] extended it to generalized the Alamouti scheme for more than two transmit antennas, called orthogonal space- time block codes (OSTBC). OSTBC have full diversity (nT - nR), but have little or no coding gain. To provide both diversity and coding gain, one can choose a space-time code that has an in- built channel coding mechanism, for example space-time trellis codes, or one can choose a space-time block code concatenated with an outer channel code. Borran et al. [4] discuss design issues of concatenating channel codes with OSTBC. They show that design issues in maximizing diversity gain, and maximizing coding gain can be decoupled. Due to this

3 Space Time Block Code is one of the techniques used in Multiple Input Multiple Output (MIMO) technologies. The other techniques are Spatial Multiplexing techniques and Beamforming techniques. Space Time Block Code (STBC) is a very simple yet very effective means of achieving transmit diversity when other form of diversity may be limited or non-existent.