China Mobile Multimedia Broadcasting Research Articles

인접 채널 간섭 제거를 통한 CMMB 수신기의 성능 향상에 관한 연구

중국의 디지털 모바일 방송 표준인 CMMB (China Mobile Multimedia Broadcasting)는 기존의 지상파 TV 방송인 Analog 방송과 동일한 주파수 대역 (474MHz ~ 754MHz)을 통해 송출되고 있다. 또한 기존의 Analog 방송의 수신 품질을 위해 디지털 방송의 송출 전력을 기존의 Analog 방송보다 낮게 하여 송출한다. 이러한 현상으로 인해 CMMB 수신기는 CMMB 수신신호와 인접하는 대역에 존재하는 Analog 방송 신호 영향을 받게 된다. 또한 셀의 경계에 있는 지역에서 CMMB 채널이 서로 인접해 있을 경우 수신기는 원하는 CMMB 신호 수신에 영향을 받게 된다. 이러한 인접 채널 간섭 (ACI : Adjacent Channel Interference)으로 인해CMMB 수신 성능에 영향을 미치며 이는 CMMB 수신기의 품질이 저하되는 문제로 이어지게 된다. 본 논문에서는 이러한 인접 채널 간섭현상을 간단하게 제거하기 위해 저주파 대역 통과 필터 (LPF : Low Pass Filter)의 차단 주파수를 조정하여 인접 채널에 의한 간섭을 최소화하였으며 이를 통해 CMMB 수신기의 수신 성능이 11.3dB 향상됨을 실험을 통해 알 수 있었다. Currently, CMMB(China Mobile Multimedia Broadcasting) and the conventional analog TV broadcasting have transmitted by using UHF(Ultra High Frequency : 474MHz~754MHz) band. Normally, the transmission power of the digital TV broadcasting is lower than the conventional analog TV broadcasting to protect the reception quality of the conventional analog TV broadcasting. The reception sensitivity of CMMB receiver has severely deteriorated due to adjacent the conventional analog TV broadcasting signals which called ACI (Adjacent Channel Interference). To improve the reception sensitivity of a CMMB receiver on ACI environment, this paper proposed a simple method which is tuning a cut off frequency of LPF (Low Pass Filter). From the experiment, the reception sensitivity of CMMB receiver was improved as 11.3dB.

Prospect of mobile TV broadcasting in China: socio-technical analysis of CMMB's development

Drawn from extensive document analysis and interviews with stakeholders, this socio-technical study examines the shaping powers of the subsystems (technology, policy/government, and market/industry) of China Multimedia Mobile Broadcasting (CMMB). After the Beijing Olympics, the first commercialized mobile TV expanded its infrastructure and business operations faster than other 3G and mobile TV broadcasting, covering 346 cities by November 2010. The findings show that CMMB, which is the leader in Chinese mobile TV development, is policy/government-driven and technologically ready. However, multiple technological standards and discrepancies between regulatory bodies slowed down its initial rollout. In the market/industry subsystem, content/services scarcity, undesirable pricing schemes, and low brand awareness are the inhibitors that curbed CMMB's diffusion. However, its strategic collaboration with China Mobile allowed it to quickly increase its user base and sale of CMMB-enabled handsets. Moreover, the socio-technical approach is a useful framework to investigate the forces that shape emerging technological trajectory holistically.

An Area-Efficient Reconfigurable LDPC Decoder with Conflict Resolution

Based on Turbo-Decoding Message-Passing (TDMP) and Normalized Min-Sum (NMS) algorithm, an area efficient LDPC decoder that supports both structured and unstructured LDPC codes is proposed in this paper. We introduce a solution to solve the memory access conflict problem caused by TDMP algorithm. We also arrange the main timing schedule carefully to handle the operations of our solution while avoiding much additional hardware consumption. To reduce the memory bits needed, the extrinsic message storing strategy is also optimized. Besides the extrinsic message recover and the accumulate operation are merged together. To verify our architecture, a LDPC decoder that supports both China Multimedia Mobile Broadcasting (CMMB) and Digital Terrestrial/ Television Multimedia Broadcasting (DTMB) standards is developed using SMIC 0.13µm standard CMOS process. The core area is 4.75mm2 and the maximum operating clock frequency is 200MHz. The estimated power consumption is 48.4mW at 25MHz for CMMB and 130.9mW at 50MHz for DTMB with 5 iterations and 1.2V supply.

An Efficient OFDM Timing Synchronization for CMMB System

An accurate and rapid synchronization scheme is a prerequisite for achieving high-quality multimedia transmission for wireless handheld terminals, e.g. China multimedia mobile broadcasting (CMMB) system. In this paper, an efficient orthogonal frequency division multiplexing (OFDM) timing synchronization scheme, which is robust to the doubly selective fading channel, is proposed for CMMB system. TS timing is derived by performing an inverse sliding correlation (ISC) between the segmented Sync sequences in the Beacon, which possesses the inverse conjugate symmetry (ICS) characteristic. The ISC can provide sufficient correlative gain even in the ultra low signal noise ratio (SNR) scenarios. Moreover, a fast fine symbol timing method based on the auto-correlation property of Sync sequence is also presented. According to the detection strategy for the significant channel taps, the specific information about channel profile can be obtained. The advantages of the proposed timing scheme over the traditional ones have been demonstrated through both theoretical analysis and numerical simulations.

Parallel LDPC decoding using CUDA and OpenMP

Digital mobile communication technologies, such as next generation mobile communication and mobile TV, are rapidly advancing. Hardware designs to provide baseband processing of new protocol standards are being actively attempted, because of concurrently emerging multiple standards and diverse needs on device functions, hardware-only implementation may have reached a limit. To overcome this challenge, digital communication system designs are adopting software solutions that use central processing units or graphics processing units (GPUs) to implement communication protocols. In this article we propose a parallel software implementation of low density parity check decoding algorithms, and we use a multi-core processor and a GPU to achieve both flexibility and high performance. Specifically, we use OpenMP for parallelizing software on a multi-core processor and Compute Unified Device Architecture (CUDA) for parallel software running on a GPU. We process information on H-matrices using OpenMP pragmas on a multi-core processor and execute decoding algorithms in parallel using CUDA on a GPU. We evaluated the performance of the proposed implementation with respect to two different code rates for the China Multimedia Mobile Broadcasting (CMMB) standard, and we verified that the proposed implementation satisfies the CMMB bandwidth requirement.

Overlapped message passing technique with resource sharing for high speed CMMB LDPC decoder

Today, demands for high speed digital communication are getting bigger due to wide deployment of 4G mobile communications and mobile TV services. Requirement for high speed data processing makes forward error correction crucial. LDPC is one of the most popular error correcting codes. In this paper, we propose a novel LDPC decoder for the China Multimedia Mobile Broadcasting (CMMB) standard. The LDPC decoding is carried out iteratively, which leads to relatively long decoding latency. Also, due to long code words, the amount of required memory is huge. To resolve these issues, we propose a novel Overlapped Message Passing (OMP) algorithm with an efficient resource sharing technique. Using the proposed method, we find the best permuted parity check matrix of the CMMB to improve the throughput while minimizing the memory requirement. Using the OMP algorithm only, we could improve the performance by 10%. To avoid potential memory access conflicts, a memory grouping technique to improve pipelining performance is also proposed. By applying all the techniques that we propose in this paper, we could improve the performance up to by 451.

An RF front-end with an automatic gain control technique for a U/V band CMMB receiver

This paper presents a fully integrated RF front-end with an automatic gain control (AGC) scheme and a digitally controlled radio frequency varied gain amplifier (RFVGA) for a U/V band China Mobile Multimedia Broadcasting (CMMB) direct conversion receiver. The RFVGA provides a gain range of 50 dB with a 1.6 dB step. The adopted AGC strategy could improve immunity to adjacent channel signal, which is of importance for CMMB application. The front-end, composed of a low noise amplifier (LNA), an RFVGA, a mixer and AGC, achieves an input referred 3rd order intercept point (IIP3) of 4.9 dBm with the LNA in low gain mode and the RFVGA in medium gain mode, and a less than 4 dB double side band noise figure with both the LNA and the RFVGA in high gain mode. The proposed RF front-end is fabricated in a 0.35 μm SiGe BiCMOS technology and consumes 25.6 mA from a 3.0 V power supply.

A low power 8th order elliptic low-pass filter for a CMMB tuner

This paper presents an 8th order active-RC elliptic low-pass filter (LPF) for a direct conversion China Mobile Multimedia Broadcasting (CMMB) tuner with a 1 or 4 MHz −3 dB cutoff frequency (f−3dB). By using a novel gain-bandwidth-product (GBW) extension technique in designing the operational amplifiers (op-amps), the proposed filter achieves 71 dB stop-band rejection at 1.7 f−3dB to meet the stringent CMMB adjacent channel rejection (ACR) specifications while dissipates only 2.8 mA/channel from a 3 V supply, its bias current can be further lowered to 2 mA/channel with only 0.5 dB peaking measured at the filter's pass-band edge. Elaborated common-mode (CM) control circuits are applied to the filter op-amp to increase its common-mode rejection ratio (CMRR) and effectively reject the large signal common-mode interference. Measurement results show that the filter has 128 dBμVrms in-band IIP3 and more than 80 dB passband CMRR. Fabricated in a 0.35-μm SiGe BiCMOS process, the proposed filter occupies a 1.19 mm2 die area.

An Improved Implementation of Debit-interleaving

Abstract This investigation was performed to reduce the number of memory unit with simply signal control comparing to PINGPONG RAM's methods of implementing debit-interleaving technique in China Mobile Multimedia Broadcasting (CMMB). Our experiment was performed by using one Single-Access RAM (SARAM) to complete real time debit–interleaving in CMMB receiver with the data rate of constellation less than half of one period of system clock. This implementation result shows that the proposed method can not only complete real time signal processing, but also saves nearly 40% of memory units comparing to the PINGPONG RAM method. It also has a signal controller simpler than Tang and Fu's does. It was concluded that the implementation, introducing in this paper, can be effectively used for debit-interleaving in CMMB receiver.

A dual-rate LDPC decoder for china multimedia mobile broadcasting systems

This paper presents an efficient VLSI architecture and implementation for LDPC decoder used in China Multimedia Mobile Broadcasting (CMMB) systems. An area-efficient layered decoding architecture based on min-sum algorithm is incorporated in the design. A novel split-memory architecture is developed to efficiently handle the weight-2 submatrices that are rarely seen in conventional LDPC decoders. In addition, the check-node processing unit is highly optimized to minimize complexity and computing latency while facilitating a reconfigurable decoding core. The proposed design is implemented using 90 nm CMOS technology with the core area of approximately 4.4 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and the standard supply voltage 1.0 V. The decoder can achieve the maximum throughput of 228 Mb/s for rate 1/2 and 342 Mb/s for rate 3/4 at 15 iterations of layered decoding. Therefore, it can be deployed on the CMMB mobile platform.

Memory efficient multi-rate regular LDPC decoder for CMMB

In this paper, we propose a memory efficient multi-rate Low Density Parity Check (LDPC) decoder for China Mobile Multimedia Broadcasting (CMMB). We find the best trade-off between the performance and the circuit area by designing a partially parallel decoder which is capable of passing multiple messages in parallel. By designing an efficient address generation unit (AGU) with an index matrix, we could reduce both the amount of memory requirement and the complexity of computation. The proposed regular LDPC decoder was designed in Verilog HDL and was synthesized by Synopsys¿ Design Compiler using Chartered 0.18 ¿m CMOS cell library. The synthesized design has the gate size of 455 K (in NAND2). For the two code rates supported by CMMB, the rate-1/2 decoder has a throughput of 14.32 Mbps, and the rate-3/4 decoder has a throughput of 26.97 Mbps. Compared with a conventional LDPC for CMMB, our proposed design requires only 0.39% of the memory.

A low power high linearity baseband for a direct conversation CMMB tuner

An analog baseband circuit made in a 0.35-μm SiGe BiCMOS process is presented for China Multimedia Mobile Broadcasting (CMMB) direct conversion receivers. A high linearity 8th-order Chebyshev low pass filter (LPF) with accurate calibration system is used. Measurement results show that the filter provides 0.5-dB passband ripple, 4% bandwidth accuracy, and −35-dB attenuation at 6 MHz with a cutoff frequency of 4 MHz. The current steering type variable gain amplifier (VGA) achieves more than 40-dB gain range with excellent temperature compensation. This tuner baseband achieves an OIP3 of 25.5 dBm, dissipates 16.4 mA under a 2.8-V supply and occupies 1.1 mm2 of die size.

Two into one may not go [mobile TV standard

The paper discusses how two organizations are competing to set the standard for mobile television in China. The prize at stake is control of an emerging market of handsets that is expected to grow very rapidly ahead of the 2008 Beijing Olympic Games. China's State Administration of Radio, Film and Television (SARFT), which runs the country's broadcasting, announced the China Mobile Multimedia Broadcasting (CMMB) standard, a satellite-based mobile TV system. However, at the end of 2006, the Standardisation Administration of the People's Republic of China (SAPRC) asked the Ministry of Information Industry (MII) to set a national standard for mobile TV, in order to create some competition.