FEC Block Research Articles

Determination of the optimal frame length of digital television broadcasting

The paper proposes a simple method for determining the optimal frame length in the DVB-T2 standard based on simple and understandable formulas based on the sequence of processing user data in the DVB-T2 standard. There should always be an integer number of FEC blocks in a T2 frame, the remaining cells that do not make up an entire FEC block will be dummy cells as a rule and represent a speed loss. As a result, the total bit rate and the depth of interleaving in the smallest details depend on the exact number of OFDM characters, and consequently, the cells in the T2 frame.

An application layer forward error correction method of wireless network broadcasting communication for smart video surveillance system

Aiming at the wireless channel in which the state of video surveillance communication network changes dramatically, to ensure the video impact under a restricted channel bandwidth condition, an application layer forward error correction system for wireless video communication is proposed. This scheme is an improved forward error correction algorithm. The most appropriate redundancy amount is implemented for each FEC block by constantly altering the redundancy in FEC blocks. Firstly, the system describes and implements the optimum video transmission. Then, the RCPC code and Raptor code are used as forward error correction codes in physical layer and application layer respectively, in this way, the optimal system solution can be acquired. In the forward error correction technology, a feedback mechanism is then developed between the receiver and the sender, which will acknowledge that the receiver can extract the packet loss rate from the received speech signal in the current network state in real time, and then the packet loss rate will be transferred back to the sender by the feedback mechanism. The sender can modify the forward packet loss rate according to the packet loss rate. The error-correcting schema can help the next speech signal have the most appropriate forward error-correcting redundancy, reducing bandwidth waste, significantly improving the adaptability and efficiency of forward error-correcting technology in the wireless network. The simulation results show that the average video quality of the proposed scheme is 0.5–4 dB higher than that of the equal error protection scheme and the extended window unequal error protection scheme.

터보부호화된 새로운 T-DMB 시스템 제안 및 성능 분석

Eureka 147 디지털오디오방송(DAB) 시스템은 CD 품질의 오디오 전송을 위하여 유럽에서 개발되었으나 한국에서는 이러한 DAB 시스템을 기반으로 하여 오디오뿐 만 아니라 비디오 신호도 전송할 목적으로 지상파 디지털 멀티미디어방송(T-DMB) 시스템을 개발하였다. 이러한 T-DMB 시스템의 성능 향상을 목적으로 본 논문에서는 양립성을 위해 기존 T-DMB 시스템 표준안에 정의된 펑쳐링 절차와 평처링 벡터를 이용하면서 터보 부호가 적용된 2가지 형태의 새로운 터보부호화된 T-DMB 시스템 모델을 제시한다. 첫 번째 모델 (Type 1)은 기존의 RS 코드, 콘볼류션 인터리빙, RCPC 코드를 터보코드로 대체시킨 것이며 두 번째 모델(Type 2)은 기존 RCPC 만을 터보부호로 대체시킨 모델이다. 시뮬레이션 결과 제안된 모델은 단지 2회 반복만으로도 상당한 성능 향상을 얻을 수 있음을 알 수 있었으며 또한 두 번째 모델은 첫 번째 모델에 비해 약간 우수한 성능을 보이고 있다. The DAB system was designed to provide CD quality audio and data services for fixed, portable and mobile applications with the required BER below <TEX>$10^{-4}$</TEX>. However for the T-DMB system with the video service of MPEG-4 stream, BER should go down <TEX>$10^{-8}$</TEX> by adding FEC blocks which consist of the Reed-Solomon (RS) encoder/decoder and convolutional interleaver/deinterleaver. In this paper we propose two types of turbo coded T-DMB system without altering the puncturing procedure and puncturing vectors defined in the standard T-DMB system for compatibility. One(Type 1) can replace the existing RS code, convolutional interleaver and RCPC code by a turbo code and the other one (Type 2) can substitute the existing RCPC code by a turbo code. Simulation results show that two new turbo coded systems are able to yield considerable performance gain after just 2 iterations. Type 2 system is better than type 1 but the amount of performance improvement is small.

Efficient coupled PHY and MAC use of physical bursts by ARQ-enabled connections in WiMAX/IEEE 802.16e networks

In this paper we address an aspect of the mutual influence between the PHY layer budding blocks (FEC Blocks) and the MAC level allocations in the Uplink and Downlink of IEEE 802.16e/WiMAX networks. In these networks it is possible to transmit MAC level frames, denoted MAC PDUs, such that a PDU contains an integral number of fixed size Data Blocks. PDUs are transmitted over PHY Bursts, which are divided into FEC Blocks. We suggest several algorithms to compute the best way to define PDUs in a Burst in order to maximize several performance criteria. We also give guidelines on how to choose the best Modulation/Coding Scheme (MCS) to use in the Burst, given the SNR of the channel and the performance criteria.

Efficient coupled PHY and MAC use of physical Bursts in WiMAX/IEEE 802.16e networks

We address several issues related to the efficient use of Bursts in WiMAX/IEEE 802.16e systems. We look on the relation between the PHY layer budding blocks (FEC blocks) and the allocation of MAC level frames (PDUs) over these FEC blocks. In particular, we show how to transmit a given amount of MAC level data bits over a given Burst in order to maximize the number of successfully transmitted data bits in the Burst. We also compute, given an amount of data bits to transmit, what is the Burst size that maximizes each of the following three performance criterion: the number of successfully transmitted data bits in the Burst, the maximum ratio between the number of successfully transmitted data bits to the Burst size, and the number of successfully transmitted data bits per PHY slot. For the first problem the paper shows how to optimally divide the Burst into PDUs and shows that sometimes it is more efficient to use less reliable Modulation/Coding schemes. For the second problem the paper shows that using the PHY slots efficiently is the best criterion to consider.

Towards an optimal transmission of SDUs in IEEE 802.16e WiMAX systems

In this paper we address the mutual influence between the PHY layer budding blocks (FEC blocks) and the MAC level allocations in the Uplink and Downlink of IEEE 802.16e systems, and address methods to increase the overall PHY and MAC combined efficiency. We evaluate the efficiency of several schemes for the transmission of Service Data Unit (SDU) packets through Protocol Data Units (PDUs) in physical Bursts. The optimality criterion is the Goodput. When using the Convolutional Turbo Code, Bursts are composed of FEC blocks that have a direct influence on the probability of bits being received successfully, and thus on the Goodput. In the first scheme, every SDU is transmitted as a stand-alone PDU. In the second scheme, the Burst is first divided into PDUs in a way that maximizes the Goodput, assuming the transmission of a bit stream (and not SDUs). Then the SDUs are mapped into the PDUs with possible Fragmentation/Packing. The optimal size of the PDUs is computed by an O(1) running time algorithm, an important feature because this algorithm is a part of the scheduler in the BS. The results show that when the estimation of the FEC success probability is accurate, SDUs should be mapped into optimal size PDUs in reliable channels. For unreliable channels it is better to transmit each SDU as a separate PDU. When the estimation of the FEC success probability is not accurate, it is always better to transmit SDUs as separate PDUs.

Coupled PHY, MAC and repetition scheduling in IEEE 802.16 WiMAX systems

We address some issues related to the mutual influence between the PHY layer budding blocks (FEC blocks ), the MAC level allocations, and repetition, in IEEE 802.16e/WiMAX systems, in order to increase the overall combined efficiency. We suggest three methods to use repetition: two are based on the increased transmission success probability due to the transmission and decoding of several copies of the same data, and one is based on signal adding and the decoding of one copy with a larger SNR. The last method turned out to be the most efficient one. We show quantitatively that repetition is efficient mainly in low SNRs where otherwise transmissions are not possible, and in particular in negative SNRs. However, there are cases where using repetition is more efficient than using a stronger Modulation/Coding scheme without repetition. Finally, we also show that repetition shall be used with several Modulation/Coding schemes, and not just with QPSK-1/2 as the IEEE 802.16e/WiMAX standard mandates.

Concurrent multipath transmission with forward error correction mechanism to overcome burst packet losses for delay-sensitive video streaming in wireless home networks

Wireless multimedia home servers are the next generation of home entertainment systems. The provision of high quality time-critical video streaming applications in indoor environments is very challenging due to high attenuation and interference caused by the walls and the contention in the shared wireless channel. This paper proposes a Delay-sensitive Multipath Forward Error Correction (DM-FEC) mechanism involving an estimation of available bandwidth and a mathematical analytical model with which the appropriate transmission rate, the FEC block length, and the FEC redundancy on each path in a multipath environment can be determined to solve previous problems. The DM-FEC mechanism not only selects the appropriate transmission rate and FEC redundancy on each path but also adaptively adjusts the FEC block length and concurrently sends data over multiple paths to overcome burst packet losses which otherwise can cause the video frame to be unplayable and impede the timely recovery of video information.

Advanced coupled PHY and MAC scheduling in IEEE 802.16e WiMAX systems

In this paper we address some issues related to the mutual influence between the PHY layer building blocks (FEC blocks) and the MAC level allocations in IEEE 802.16e /WiMAX systems, in order to increase the overall PHY and MAC combined efficiency. In these systems transmissions are carried in physical Bursts, both on the Uplink and Downlink channels. Bursts are composed of slots, which are grouped into FEC blocks. The number of slots in a Burst determines the length and number of the FEC blocks. The FEC blocks have a direct influence on the probability that bits are received successfully, and thus on the Burst Goodput, which is defined as the ratio between the average number of bits in the Burst that arrive successfully at the receiver, to the Burst length. In this paper we address a new coupled PHY and MAC scheduling methodology by investigating the relationship between the Burst length and its Goodput in different Modulation/Coding schemes, and investigate, given a Burst, the most efficient such scheme. The outcomes of the paper are twofold: first we show that the Goodput of a Burst is almost not dependent on its length. Second, we show that in most cases, the most efficient Modulation/Coding scheme is the one that enables us to transmit the largest number of bits in a Burst. However, there are a few cases where this is not the case. We show these cases in the paper.

Joint loss pattern characterization and unequal interleaved FEC protection for robust H.264 video distribution over wireless LAN

The recently adopted H.264 standard achieves efficient video encoding and bandwidth savings. Thus, designing communication protocols and QoS control mechanisms for H.264 video distribution over wireless IP networks is a topic of intense research interest. Delivering video streams to terminals via a wireless last hop is indeed a challenging task due to the varying nature of the wireless link. While a common approach suggests exploiting the variations of the wireless channel, an alternative is to exploit characteristics of the video stream to improve the transmission. In this paper, we combine both approaches through an efficient wireless loss characterization and a low-delay unequal interleaved FEC protection. Besides deriving new QoS metrics for FEC block allocation, the wireless loss characterization is as well used to adjust the interleaving level depending on the loss correlation exhibited by the wireless channel. This novel unequal interleaved FEC (UI-FEC) protocol allows graceful video quality degradation over error-prone wireless links while minimizing the overall bandwidth consumption and the end-to-end latency.

Adaptive code rate decision of joint source-channel coding for wireless video

A practical method of adaptive code rate decision for joint source-channel coding is proposed for wireless video. It is based on the observations that the residual error probabilities at the optimal code rates for different symbol error probabilities are closely clustered to their average value for an FEC block size n in RS(n, k) code and for a total channel rate R for both independent and bursty error models. Experimental results show that the proposed method achieves a near-optimal code rate decision in the joint source-channel coding.

Slotted ALOHA multiple access and error control coding for land mobile satellite networks

AbstractThis paper considers a satellite network with data messages being transmitted by land mobile users according to slotted Aloha multiple access. The mobile communication links suffering from multipath fading and signal shadowing are modelled as Gilbert‐Elliott channels. FEC block coding is used to correct transmission errors. The maximum achievable information throughput and the mean packet delay are derived from a combined analysis of the multiple access and FEC/ARQ protocol. The results show that the additional overhead necessary for FEC is outweighed by the benefit in throughput and delay. Finally, the capture effect and its consequences are discussed.