BER Performance

In many PAPR research works, the effect on BER is neglected. In fact, the effect on BER may be great in some cases. In our simulation, we use Nt = 2 and K = 256 subcarriers. The available bandwidth is 1MHz and the subcarrier K = 256. We consider the channel with power delay profiles: COST207[24] typical urban six-ray power delay profile. The subcarrier path gains are generated according to Eqs.(2.9), independently for different transmit and receive antennas. The oversampling factor is J = 4. All the other parameters are just the same as what we use in Section (3.4).

Fig.(4.7) and Fig.(4.8) show the performance of SS-CARI and TDCS using the

- 1 0 1 2 3 1 0^{- 4}

1 0^{- 3} 1 0^{- 2} 1 0^{- 1}

E b / N o ( d B )

BER

S S - C A R I( W = 4 )

C l i p r a t i o = 6 C l i p r a t i o = 7 C l i p r a t i o = 8 C l i p r a t i o = 9 N o C l i p p i n g

Figure 4.7: SS-CARI BER performance for W = 4.

space frequency code investigated in Section (3.3). In the simulation, we assume that CSI and side information can be recovered correctly by the receiver. Take 7dB clipping ratio case as example. We can observe that the BER performance of both schemes are around 10⁻⁴ at Eb/N0 = 3dB.

In Eqs.(4.14), multiplying unitary matrix U to the left side of a space-frequency codeoword will not effect the BER performance. Hence the U can be designed by any unitary matrix other than that shown in Eqs.(4.15)

- 1 - 0 . 5 0 0 . 5 1 1 . 5 2 2 . 5 3 1 0^{- 4}

1 0^{- 3} 1 0^{- 2} 1 0^{- 1}

E b / N o ( d B )

BER

T i m e - d o m a i n s c h e m e ( Q = 1 6 )

C l i p r a t io = 6 C l i p r a t io = 7 C l i p r a t io = 8 C l i p r a t io = 9 N o C li p p i n g

Figure 4.8: TDCS BER performance for Q = 16.

Side Information Embedded

In some situations, the side information is embedded into the system. There are many methods to embed the side information into the system. A major concern is that the side information must be well protected. Otherwise, serious error propagation will occur. Here, we consider a simple method which is obtained by inserting the side information into the zero terms of Eqs.(3.14) and Eqs.(3.15) and each reserved subcarrier contains one side information bit. In fact, we can insert more than one bit to one subcarrier if the system needs a large number of the side information bits.

In order to protect the side information bit, the power of side information signals is transmitted four times of original signals. The performance of SS-CARI scheme

remain similar to TDCS scheme, shown in Fig.(4.9) and Fig.(4.10). Take the 7dB clipping ratio condition as example, we can observe that the BER performance of both schemes are around 10⁻⁴ at Eb/N0 = 3dB. That is, the system suffers no BER performance degradation by inserting the side information bits in the simple methods described above.

- 1 - 0 . 5 0 0 . 5 1 1 . 5 2 2 . 5 3 3 . 5

1 0^{- 4} 1 0^{- 3} 1 0^{- 2} 1 0^{- 1}

E b / N o ( d B )

BER

S S - C A R I( W = 4 )

C li p r a t i o = 6 C li p r a t i o = 7 C li p r a t i o = 8 C li p r a t i o = 9 N o C l i p p i n g

Figure 4.9: SS-CARI BER performance for W = 4 with side information embedded.

- 1 0 1 2 3 1 0^{- 4}

1 0^{- 3} 1 0^{- 2} 1 0^{- 1}

E b / N o ( d B )

BER

T i m e - d o m a in s h c e m e ( Q = 1 6 )

C l i p r a t io = 6 C l i p r a t io = 7 C l i p r a t io = 8 C l i p r a t io = 9 N o C li p p in g

Figure 4.10: TDCS BER performance for Q = 16 with side information embedded.

CONCLUSIONS AND SELF EVALUATION

In this three-year project, our goal is to investigate MIMO-OFDM systems so that both low PAPR and error rates can be achieved. In the first year, we investigate a space-frequency code with two transmit antennas that is constructed by the concate-nation of binary LDPC code and the Alamouti space-time coding. The reason for choosing such a design is that this construction can achieve large column distance and full rank of the codeword difference matrix, which will ensure large diversity for combating the multi-path fading MIMO-OFDM channel. Simulation results ver-ify that the construct space-frequency code does perform well in the MIMO-OFDM channel. Based on this efficient space-frequency code, we propose a low complexity

47

selective-mapping type PAPR reduction technique. In the proposed technique, the candidates are generated in the time-domain instead of the frequency domain. Thus, only two IFFT operations are needed in the proposed technique while for the selec-tive mapping using frequency domain many IFFT operations are needed. In case the number of candidates is not great (no more than 16), the proposed technique can significantly reduce the complexity without sacrificing the PAPR reduction capabil-ity and error rates. Simulation results verify the advantage of the proposed PAPR reduction technique.

Some of the results of this research comes from the PhD thesis of S.K. Deng [25]

and the master thesis of Y. H. Lo [27]

As a summary, we have a very significant research result in this first-year term, i.e., the time-domain PAPR reduction technique for the MIMO-OFDM system. The idea is novel and the advantage is obvious in case the number of selective mapping is not large. We believe that this result can be published in prestigious academic conferences and journals.

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