# Averting BER Floor with Iterative Source and Channel Decoding for Layered Steered Space-Time Codes
## 2 Overview of Layered Steered Space-Time Codes
### Transmitter Model  
Figure 1 depicts the block diagram of our proposed scheme. The LSSTC architecture shown in Figure 1 utilizes \(N_{t}=4\) transmit AAs. The geometry of AA is discussed in [34] for enhancing the capacity of a wireless system. For the purpose of attaining transmit diversity via independent fading experience of each AA, they are placed at sufficient distance apart from one another. Each AA contains \(N\) elements which are typically spaced at a distance of \(d=\lambda/2\) from one another, where \(\lambda\) represents the carrier's wavelength. This spacing among the \(N\) elements is beneficial for introducing beamforming gain. On the receiving side, there are 4 antennas which effectively receives the signal from the wireless channel. The information is serial-to-parallel converted and the resulting symbol streams are then independently allowed to the corresponding STC with multiple AAs as discussed in [33]. The information bits are initially encoded by the HEVC encoder, and the data are compressed to an extent suitable for limited bandwidth transmission. HEVC/H.265 encoder is the latest standard adopted by researchers across the world and approved by The International Telecommunication Union-Telecommunication (ITU-T) standardization sector. The H.265 standard was particularly developed to enhance the compression efficiency of Advanced Video Coding (AVC)/H.264 standard, with the consistent video quality in both standards [37]. It is worthy to mention that this compression efficiency is attained at the expense of increased computational techniques, rendering the source encoding more complex [38; 39]. The H.265 encoder works by removing the temporal as well as spatial redundancy, hence it is regarded as a hybrid source codec [39]. Due to the higher compression techniques employed in H.265 encoding, the encoded streams are more vulnerable to the bit errors induced by channel propagation. Therefore, considerable degradation in the perceived visual quality is observed with even single-bit error. Hence, to mitigate the burst of errors in the H.265 encoded video stream, more efficient error protection and correction techniques need to be incorporated in the source encoded stream. The source encoded stream \(x_{k}\) is forwarded to the SBC encoder employing rate-1/3 which generates the stream \(s\). The proposed low-complexity SBC encoder works perfectly well with the low-complexity STCs. An interleaver is invoked just after the SBC encoder  
Figure 1: Block diagram of the three-stage LSSTC scheme with iterative JSCD system. which is labelled as \(\Pi_{\text{out}}\) in Figure 1, and the stream is then allowed to pass through the URC encoder [14]. Most often an interleaver is deployed before modulating the encoded stream over a wireless channel [14], and we have depicted that second interleaver as \(\Pi_{\text{in}}\) in Figure 1. We have used SP modulator for the purpose of exploiting the joint space-time symbols of the LSSTC scheme by efficient selection of single point [7]. Furthermore, the SP modulator is very much beneficial for the best possible minimum Euclidean distance in the real-valued space for constructing efficient error correcting codes [23]. Our system works on 4-dimemsional SP design as we have considered a scheme utilizing two STCs, namely STC1 and STC2 in Figure 1. More explicitly, the system will choose only from \(L_{SP}\) number of legitimate SP mapped available vectors for transmission over the two STCs using AAs. According to [14], the SP modulator maps each of the total number of \(B\) binary coded bits such that each SP mapped symbol contains \(log_{2}(L_{SP})\) bits. In our case, \(B=log_{2}(16)\) yields 4 channel coded bits for each SP symbol. Furthermore, a normalised Doppler frequency of 0.01 for the correlated Rayleigh fading channel is considered. More specifically, the correlated Rayleigh fading channel is considered useful for realistic wireless communication where multipath exist [23].