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Abstract--- Multiple input, multiple output with orthogonal frequency division multiplexing (MIMO-OFDM) is used in 4G and 5G. it combines Multiple Input, Multiple Output technology, which transmitting the information over multiple antennas, and OFDM technique, which divide the channels orthogonally to provide reliable communication at high data rate. In order to achieve high data rate STBC technique is used in MIMO system. For encoding and decoding alamouti code is introduced. In STBC alamouti code is introduced this is basic for STBC and the information is transmitted through two different antennas this will reduce interference. Self-heterodyne is combined with the MIMO-OFDM system which uses SCP technique to move information from one carrier frequency channel to another and this will eliminates phase noise. With MIMO -OFDM and self-heterodyne relay is added due to increase the coverage area and mean square estimation calculate BER and SNR performanceIndex Term---STBC, Alamouti code, phase noise, SCP technique, BER, SNR, and MIMO-OFDM, self-heterodyne.
I. INTRODUCTION
In telecommunication networks, a channel access method or multiple access method allows several terminals connected to the same multi-point transmission medium to transmit over several terminal and to share its capacity. Example of shared physical media or wireless networks, bus networks, ring networks and half duplex point to point links.
A channel access strategy is based on a multiplexing approach that allows signals to share the same communication channel medium. Multiplexing is provided by the physical layer. The channel access methods are TDMA, FDMA, CDMA and OFDM. FDMA system used in the first-generation (1G) cell-phone systems, where each phone call was assigned to specific uplink frequency channel, and another downlink frequency channel. TDMA is used in digital 2G cellular systems such as global system for mobile communications (GSM). CDMA is used for 3G system. The advantage of FDMA is OFDM which is used in 4G.
A system is distinguished by how it responds to input signals. This system has one or more inputs and outputs. Depending on the inputs and outputs it is categorized as SISO, SIMO, MISO and MIMO, these systems are used for fast transmission. MIMO has high channel capacity than other system.
Self-heterodyne OFDM is known to give complete immunity beside frequency-offset and phase noise [1], with a much lower RF frontend complexity, when compared to standard OFDM techniques. A subcarrier pairing method improves the overall error performance of self- heterodyne OFDM communications [2]. The proposed pairing scheme escapade the average signal-to-interference-to noise ratios (SINRs) bias experienced among self-het OFDM subcarriers. Consider two improvements for self-heterodyne OFDM (Self-Het OFDM): subcarrier pairing and smart carrier positioning (SCP) [3], study their performance over a practical 60 GHz indoor RF channel. The improved orthogonal frequency division multiplexing (OFDM) baseband processor take on adaptive modulations to grouped subcarriers, and its demonstration in millimeter-wave wireless indoor links [4]. Recent changes in how people consume multimedia services are causing an unstable increase in mobile traffic [5].The receiver space diversity based on millimeter wave (longer than infrared waves but shorter than radio waves) self-heterodyne transmission technique is demonstrated and its effective gain in two-path channel environments is theoretically and experimentally characterized [6]. Measure record voltage response time in test circuits, up to 8,000 mV/mW from 75 to 93 GHz, with input power from 50 to30 dBm. The system was applied to a 60-GHz-band transmission system for the first time [7].It describes the first time experimental studies on 60-GHz band transmissions of terrestrial digital broadcasting signals (ISDB-T) with 64QAM modulations on coded orthogonal frequency division multiplexing (COFDM) format [8].Millimeter-wave OFDM wireless personal area network system applying adaptive modulation for grouped sub- carriers was newly developed [9].
In the existing system only the self-heterodyne is added to MIMO-OFDM. This will reduce only 3.5dB of BER. The throughput efficiency is less it delivers only less number of information over communication channel. Interface is more because of using Multiple Input Multiple Output antennas. Edge of the base user cannot get the clear signal because at the end of base station the signal strength is low and also it uses golden code[10[ this will create phase noise and not suitable for relay based system. In this paper we introduce a relay based system with MIMO-OFDM using self-heterodyne this will reduce the error rate and also the interference because of using alamouti code [11].
II. SYSTEM MODEL
A. MIMO SYSTEM
At one time in wireless MIMO is used only the theoretical purpose in both transmitter and receiver. But in modern usage “MIMO” specially used to a practical technique for sending and receiving more than one data signal on the same radio channel at the same time through multipath propagation. MIMO is fundamentally different from smart antenna a technique is specially developed to enhance the performance of a single data signal, such as beam forming and directivity.
MIMO can be classified into three forms they are precoding, spatial multiplexing and diversity coding. Precoding is multi-stream beam forming in the narrowest definition and, it is considered to be all spatial processing that occur at the transmitter. Spatial multiplexing requires MIMO antenna configuration. In spatial multiplexing, several high-rate signals is split into multiple lower-rate streams and each of this lower rate streams are transmitted from a different transmit antenna in the same frequency channel. Diversity coding techniques are used when there is no channel knowledge at the transmitter. In diversity methods, a single stream is transmitted, but the signal is coded using techniques called space time coding. The signal is emitted from each of the transmit antennas with full or near orthogonal coding.
In MIMO system STBC code[13] is used because it transmit multiple copies of a data stream across a number of antennas and to exploit the various received version of data to improve the reliability of data-transfer and also it avoid interference.
B SPACE-TIME BLOCK CODES
Space-time block codes (STBC) are orthogonal and can achieve full transmit diversity specified by the number of transmit antennas. The concept of space-time coding has start from diversity techniques using smart antennas. By using data coding and signal processing at both sides of transmitter and receiver, space-time coding now is more effective than traditional diversity techniques. The data are create as a matrix format which has its columns this columns are equal to the number of the transmit antennas in MIMO and its rows are equal to the number of the time slots required to transmit the data during transmission. At the receiver side, the signals received are first combined and then sent to the maximum likelihood detector where the decision rules are applied. For encoding alamouti code is used.
C. Alamouti scheme
Alamouti scheme is the basis of the Space Time Coding method. The mathematical explanation of the scheme with two transmitting and two receiving antennas is also explained here. In this work, a two-branch transmit diversity scheme is implemented. Using two transmit antennas and two receive antenna, the scheme provides the high diversity gain. The scheme may easily be generalized to two transmit antennas and M receive antennas to provide a diversity order of 2M. At the transmitter side, a block of two symbols is taken from the source data and sent to the modulator. After that, Alamouti space-time encoder takes the two modulated symbols, in this case called s1 and s2 creates encoding matrix S where the symbols s1 and s2 are mapped to two transmit antennas in two transmit time slots.
Multiple input, multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) is the dominant air interface for 4G and 5G broadband wireless communications. It combines multiple input, multiple output (MIMO) technology, which multiplies capacity by transmitting different signals over multiple antennas, and orthogonal frequency division multiplexing (OFDM), which divides a radio channel into a large number of closely spaced sub channels to provide more reliable communications at high speeds. Research conducted during the mid-1990s showed that while MIMO can be used with other popular air interfaces such as time division multiple access (TDMA) and code division multiple access (CDMA), the combination of MIMO and OFDM is most practical at higher data rates. The main motivation for using OFDM in a MIMO channel is the fact that OFDM modulation turns a frequency-selective MIMO channel into a set of parallel frequency-flat MIMO channels. This renders multi-channel equalization particularly simple, since for each OFDM-tone only a constant matrix has to be inverted.
In order to increase the signal strength the self-het is added to MIMO-OFDM.
III. MIMO-OFDM USING SELF-HET
our scheme using SCP outperforms the Alamouti coded MIMO-OFDM with super-heterodyne structures at high SNRs. Similar behavior is observed for the Golden coded MIMO self-het OFDM Compared to Alamouti code, the Golden code is more sensitive to the phase noise[12], and the error floor occurs at lower SNRs. Hence, Golden coded MIMO self-het OFDM outperforms the conventional MIMO-OFDM at practical SNRs ranges. The phase noise is avoided with the help of alamouti code in MIMO-OFDm with heterodyne.
IV. MIMO WITH RELAY PATH ANALYSIS
Relay is combines with self-het MIMO-OFDM system this will increase the number of users. We use forward decode relay. The decode-and-forward relay protocol is a protocol defined for wireless cooperative communications. An example of a wireless communication network in which cooperation improves the performance of the system is the relay network.
The relay decodes and re-encodes the received signal, and then it forwards it to the destination. This processing of the signal at the relay is also known as making a hard decision, as the information sent by the relay does not include any additional information about the reliability of the source-relay link. When encoded modulation is used this protocol is also known as Detect-and-Forward as the processing of the relay is detection of the signal. This relay increase the coverage area and also edge of the base station user get clear signal. Multiple-input multiple-output (MIMO) relay systems provide the high capacity of MIMO communication with the coverage extension capability of relay transmission.
V. SIMULATION RESULTS
In this section we simulate BER performance of 2 x 2 MIMO-OFDM using self-het on relay path analysis for the parameter of bit error rate and signal to noise ratio.
The 2X2 MIMO self-het OFDM for 16bit QAM is shown in fig 5. The input data chosen as random pilot values as 2, 3&4 were mapped into 16QAM constellation. MIMO OFDM multicarrier transmission was carried out using MATLAB application. The received bit were compared with transmitted bits in order to calculate the BER in terms of percentages, for each signal to noise power ratio. The simulation was carried out by BER versus SNR performances.
VI. CONCLUSION
The 2X2 MIMO Self-Het OFDM system provided with 16 bit data. In that, the Alamouti code sequence with Self-Het Pilot insertion ‘P’ was chosen as random values as 2, 3 &4. The BER versus SNR for different bit values for 2X2 MIMO Self-Het system was completed and the performance of the system was compared. From the values obtained it is found that the BER Vs SNR 16QAM is the lowest signifying high performance with no phase noise by Self-Het. With the help of forward decode relay it reduces 3.8 dB of BER using alamouti code sequence