International Journal of Computer Trends and Technology (IJCTT) – volume 7 number 4– Jan 2014
MIMO Schemes With Spatial Modulation in Wireless Communication Laxminarayanan.G1, Jayanthi.S 2 1
(Electronics And Communication Engineering,Sri Manakula Vinayagar Engineering College/Pondicherry University,India) 2 (Electronics And Communication Engineering,Sri Manakula Vinayagar Engineering College/Pondicherry University,India)
ABSTRACT : The combination of spatial modulation (SM) and space-time block coding (STBC) provides more advantages than other modulation techniques. In the MA-SM system, the transmitted symbols are mapped into a high dimensional constellation space including the spatial dimension. This provides Inter channel Interference between the signals while signals are transmitted by MIMO scheme in which receiver receives many signals and it also causes high BER (Bit Error Rate). A general principle for designing the efficient MA-SM for arbitrary number of transmits antennas and different modulation schemes are adopted. Moreover a near optimal detection scheme with low complexity for MA-SM is also used and analyzed. This may reduce the Inter channel Interference and bit error rate efficiently.
Keywords - Include spatial modulation (SM), multiple active spatial modulation (MA-SM), multiple-input multiple-output (MIMO), space-time block coding (STBC), V-BLAST systems.
1. INTRODUCTION MULTIPLE-INPUT multipleoutput (MIMO) scheme designed for wireless communication is shown to be a good process to increase the capacity and reliability comparing with wireless systems .Among the several MIMO techniques, The diversity and multiplexing gain are achieved by space time block codes(STBC) and spatial multiplexing respectively. The STBCs provides a good way to improve spatial diversity gain because of the implementation simplicity and also low decoding complexity. The V-BLAST scheme can give high multiplexing gain. The most eligently used V-BLAST scheme can provide a increased multiplexing gain by allowing continuous transmission over all antennas. The high capacity is obtained by joint ML decoding for the data streams at the receiver, but the complexity grows
ISSN: 2231-2803
exponentially with the number of streams. However, the available linear sub-optimal decoders for V-BLAST, such as linear decorrelator, successive cancellation and linear minimum mean square error (MMSE) have shown to loss the error performance of the system . The transmission of a signal in MIMO scheme from a transmitter can be received by various receivers. While transmitting the signals using this scheme there will be inference occur between the signals received in the receiver end. This is due to receiving more than one signal at a time. In order to avoid this situation, this paper proposed a design which describes the usage of multiple modulation techniques like 16QAM, QPSK, BPSK, 8PSK, etc. For instance the signal from a transmitter with modulation technique QPSK can be received only by means of the receiver with the same modulation technique.
2. PROPOSED SCHEME The proposed design which describe the implementation of different modulation techniques in wireless transmission system as shown in the block diagram figure 1. 2.1 STBC (Space Time Block Codes) In STBC scheme both the transmitting antenna indices and STBC symbols from which these symbols will be carry information. We choose Alamouti’s STBC, which transmits one symbol pcu, as the core STBC due to its advantages in terms of spectral efficiency and simplified ML detection. In Alamouti’s STBC, two complex information symbols (�1 and �2) drawn from an �PSK or �-QAM constellation are transmitted from two transmit antennas in two symbol intervals in an orthogonal manner by the codeword where columns and rows correspond to the transmit antennas and the symbol intervals, respectively. For the STBC-SM scheme we extend the above matrix to the
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International Journal of Computer Trends and Technology (IJCTT) – volume 7 number 4– Jan 2014
Fig. 1 Block diagram of the proposed Design corresponding graphical representation is shown antenna domain. An STBC is usually represented in the figure 2. by a matrix. Each row shows a time slot and each column shows one antenna transmissions over time. TABLE I CARRIER PHASE AND AMPLITUDE CORRESPONDING TO THE VARIOUS SYMBOLS TRANSMITTED
Here, Sij is the modulated symbol to be transmitted in time slot i from antenna j. There are to be T time slots and nT transmitter antennas as well as nR receiver antennas. This block is usually named to be of 'length' T. 2.2 QAM MODULATION The 16-QAM means 16-state Quadrature amplitude modulation. In which four I values and four Q values, giving four bits per symbol, 16 states because row (2,4) = 16. Theoretical bandwidth efficiency is four bits/second/Hz .I and Q channels are spitted by data in which it takes on two phases. However, two intermediate amplitude values will be accommodated by 16 QAM. Two bits are routed to each channel simultaneously. In each channel the two bits are added and then it is fed to the channel’s modulator. Phase modulation (analogue PM) and phase-shift keying (digital PSK) can be regarded as a special case of QAM, where the magnitude of the modulating signal is a constant, with only the phase varying. This can also be extended to frequency modulation (FM) and frequency-shift keying (FSK), for these can be regarded as a special case of phase modulation. Table I shows the details regarding the carrier phase and amplitude corresponding to the various symbols transmitted. And the
ISSN: 2231-2803
Symbol transmi tted 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001 1010 1011 1100 1101 1110 1111
Carrier phase
225º 255º 195º 225º 135º 105º 165º 135º 315º 285º 345º 315º 45º 75º 15º 45º
Carrier Amplitu de 0.33 0.75 0.75 1.0 0.33 0.75 0.75 1.0 0.33 0.75 0.75 1.0 0.33 0.75 0.75 1.0
2.3 QPSK MODULATION In QPSK, the symbols are grouped and modulated by data bits and each can take one of four possible values. In each interval, the modulator will be shifting the carrier to one of four possible values corresponding to the symbol of input values. In the ideal case, the phase shift will be 90 degree apart and this phase can be equal selected by it. The structure uses the trigonometric identity, I cos ωct + Q sin ωct = R cos (ωct + θ)
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International Journal of Computer Trends and Technology (IJCTT) – volume 7 number 4– Jan 2014
TABLE II
Where
PHASE SHIFT DURING STATE CHANGE IN QPSK Phase Change (Degree s) 0 90 180 270
State Change
Dibit
A-to-A A-to-B B-to-D D-to-C
01 00 10 11
2.4 DESCRIPTION OF THE PROPOSED SCHEME
Fig. 2, 16 QAM Mapping
The modulated signal for carrier frequency, x(t) = I (t) + jQ(t) The trivial model of the modulator will be requiring the simulation of the idealized signal. The complex signal x(t) can be created by simplification using the in phase baseband signal I(t) as the real part. The schematic diagram for the representation of QPSK mapping is in figure 3. The transmission of symbols in QPSK corresponding the various state change and phase changes are described in Table II.
The transmission of a signal in MIMO scheme from a transmitter can be received by various receivers. While transmitting the signals using this scheme there will be inference occur between the signals received in the receiver end. This is due to receiving more than one signal at a time. In order to avoid this situation, this paper proposed a design which describes the usage of multiple modulation techniques like 16QAM, QPSK, BPSK, 8PSK, etc. For instance the signal from a transmitter with modulation technique QPSK can be received only by means of the receiver with the same modulation technique. And also the input signals are split in order to transmit the segmented input signal at a particular time slot by means of STBS system.
3.CHANNEL ESTIMATION Let Ep and Np be the energy transmitted for each pilot pulse and the number of pilot pulses used for channel estimation, respectively. Similarly we can be assuming that channel estimation is shown by using a Maximumlikelihood detector,then by obserbing Np pilotplus-data symbols,the wireless channel will be constant. In transmission of one block of pilot– plus–data symbols, the wireless channel is assumed to be constant, i.e. a quasi–static channel model is considered. The channel estimation errors are statistically independent and identically distributed, as well as statistically independent of the channel gains and the AWGN at the receiver.
4.DETECTION In MA-SM (Multi Active Spatial Modulation), the different transmission symbols are transmitted by means of different transmission antennas. In the MA-SM system, the receiver must solve the
-
Fig. 3 QPSK Mapping
ISSN: 2231-2803
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International Journal of Computer Trends and Technology (IJCTT) – volume 7 number 4– Jan 2014
hypothesis problem with the proper algorithm. The optimal ML decoder, which detects the antenna set together with the symbols, increases exponentially in complexity for high order constellation since the exhaustive search space increases at the speed of as NP grows. We will introduce a near-optimal detection method with low complexity for MA-SM scheme. Considering the signal transmission model and assuming that the indices of active antennas are a1…..aNP, we could rewrite it following equation to simplify notation. This will be giving the linear structure of the signal space that the received signal y is the linear combination of the channel vector corresponding to the active antennas. Fig. 4, 16-QAM Demodulation If the noise could be ignored, y lies in the subspace Gk spanned by ha1 , ...hNP . Supposing that the dimension of Gk is pk, we can judge whether the vector is in the subspace or not via projecting y onto the subspace Gk to derive the vertical distance between them. Since projection is a linear operation, we can represent it using a pk by NR matrix Tk, the rows of which form an orthogonal basis of Gk. The vector y − Tky should be interpreted as the vertical distance from the vector y to subspace Tk, but expressed in terms of the coordinates defined by the basis of Gk formed by the rows of Tk. Based on Tse’s decorrelator described in [8], the decorrelator for the kth stream Tk is the k-th row of the pseudo inverse H† of matrix H is given by,
The resulting "List-SDR" demodulators require one semi-definite program (SDP) to be solved at each demodulation decoding iteration. In the proposed "Single-SDR" demodulator this requirement is reduced to one SDP per channel use by deriving an approximation of the randomization procedure used by the List-SDR demodulator and showing that this approximation enables the decoupling of the processing of the channel measurement from that of the extrinsic information from the decoder. Simulation results show that the proposed demodulators provide considerable reductions in computational cost over several existing soft demodulators, and that these reductions are obtained without incurring a substantial degradation in performance. The performance of the 16 QAM Demodulation is given by the plotting the graph SNR vs BER and it is shown in the fig.4. 4.2 QPSK DEMODULATION
4.1
16 QAM DEMODULATION Three computationally-efficient listbased soft MIMO demodulators are developed, each on generates its list using the randomization procedure associated with the semi-definite relaxation (SDR) of a particular hard demodulation problem. The schematic of this SDR depends on the signalling scheme .Let us now focus on 16-QAM signalling. The key step in the development of the first two demodulators is the derivation of polynomial expressions for the extrinsic information provided by the decoder. The decoder will be equally provided with respect to the corresponding values which will be equally dependent in its values and this values will show low dependent values where it does not have equal ant values with respect to the signalling data in it. These expressions enable this information to be incorporated into the SDR framework.
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The original message data stream is assumed by the QPSK modulator that it was split into two streams, A and B, at the transmitter, with each being converted to a PSK signal. The two PSK signals were then added their carriers being in phase quadrature . There are two PSK de-modulators in the de-modulators , whose outputs, after analog-todigital (A/D) conversion, are combined in a parallel-to-serial converter.so,the recombination of the two channels to the original single serial stream is performed by the convertor. Here it can be done, if the carriers at the carriers at the demodulator are synchronous ,and correctly phased, with respect to the transmitter
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International Journal of Computer Trends and Technology (IJCTT) – volume 7 number 4– Jan 2014
6.CONCLUSION In this paper, we introduced a novel high-rate, low complexity MIMO transmission scheme, called MA-SM, as an alternative in existing techniques in which, STBC, SM, VBLAST and implementation of different modulation techniques. It has been shown via computer simulations that MA-SM offers significant improvements of system performance with compared to the different modulation with an acceptable linear decoding complexity. It can be concluded that the MA-SM scheme will be useful in wireless communication. The future research work is focused on design a system such that the system itself adopt the modulation based on the type of input.
Fig. 5 ,QPSK Demodulation In this experiment only the principle of recovering the A and B channels from the QPSK signal is demonstrated. So neither the A/D nor the parallel-to-serial converter will be required. Since you will be recovering these signals separately only one half of the demodulator need be constructed. The PHASE SHIFTER with appropriate adjustment will recover either A or the B message .The BER curve for QPSK demodulation is shown in fig.5
5.SIMULATION PERFORMANCE In order to substantiate the theoretical derivation as shown in Figure 6, the BER performance by Monte Carlo simulation transmission with different numbers of receives antennas. It could be observed that the derived BEP bound agrees well with the simulation results at high SNRs while the mismatch at low SNRs is because that some approximation premise in the theoretical derivation cannot be satisfied.
Fig. 6 BER Vs SNR
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