Apparatus (130) and method for receiving a QAM signal using a backward compatible hierarchical coding scheme to increase data transmission using finer constellations, while maintaining compatability with existing Direct Broadcasting Satellite (DBS) systems. The apparatus employs multiple stages of decoders (146,170) such that the finer constellations of the QAM signal are unraveled at different stages.

Apparatus and method for processing a quadrature amplitude modulated (qam) signal

A television receiver for processing both analog and digital television signals. Specifically, the television receiver contains a RF/IF front end (202), an analog-to-digital converter that samples near baseband signals using a free running sampling rate, and a combined demodulator. The combined demodulator recovers both pilot and pix carriers as well as provides a passband adaptive equalizer (208) that removes ghosts from analog television signals and intersymbol interference from digital television signals.

Multiple modulation format television signal receiver system

A receiver is arranged for receiving a transmitted quadrature amplitude modulated (QAM) signal representing successive symbols, and including an in-phase (I) component and a quadrature (Q) component. In such a receiver, a timing recovery system includes a source of samples representing the QAM signal produced at a fixed frequency. A first chain of processing circuitry for the I component includes a first demodulator, coupled to the sample source, for demodulating the I component of the QAM signal to baseband; and a first interpolator, coupled to the first demodulator and responsive to a control signal, for producing I component samples taken at times synchronized to the transmitted symbols. A second chain of processing circuitry for the Q component includes a second demodulator, also coupled to the sample source, for demodulating the Q component of the QAM signal to baseband; and a second interpolator, coupled to the second demodulator and responsive to a control signal, for producing Q component samples taken at times synchronized to the transmitted symbols. A phase error detector is coupled to the first and the second interpolators, and detects the phase error between the sample times of the I and Q component samples from the first and second interpolators and times of the successive transmitter symbols. A summer is coupled to the phase error detector and a source of a nominal delay signal. A numerically controlled delay circuit, is coupled to the summer, for producing the respective control signals for the first and second interpolators.

Digital variable symbol timing recovery system for QAM

A receiver (100) for demodulating multiple digital modulation formats including vestigial sideband (VSB), quadrature amplitude modulation (QAM), and offset QAM (OQAM). The receiver includes a timing recovery circuit (126) that produces accurate timing information for each modulation format and a signal processor (54) for adaptive equalization and quantization of each modulation format. The signal processor includes an adaptive equalizer (900) which is a passband equalizer that performs blind equalization using a feed forward equalizer (902) and a decision feedback equalizer (910).

Receiver capable of demodulating multiple digital modulation formats

A television signal receiver for processing an HDTV signal transmitted in a vestigial sideband (VSB) format includes input complex filters shared by a timing recovery network (30) and a carrier recovery network (50). The filter network includes a pair of upper and lower band edge filters (20, 22) mirror imaged around the upper and lower band edges of the VSB signal for producing suppressed subcarrier AM output signals. The timing recovery network includes a phase detector (28, 38, 62) and responds to an AM signal derived from the two filters (via 26) for synchronizing a system clock (CLK). The carrier recovery network (50) also includes a phase detector (54, 60, 62, 64), and responds to outputs from one or both of the filters for producing an output error signal (Δ) representing a phase/frequency offset of the VSB signal. The error signal is used to reduce or eliminate the offset to produce a recovered baseband or near baseband signal. A subsequent equalizer eliminates any residual phase offsets in the recovered signal.

Carrier independent timing recovery system for a vestigial sideband modulated signal

The authors present system design considerations and simulation results for a receiver prototype for QAM (quadrature amplitude modulation)-based digital HDTV (high-definition television) systems in the context of current standard deliberations for terrestrial broadcasting. Efforts were concentrated on design choices of the receiver sub-systems for adaptive equalization, and carrier and symbol timing recovery. System performance evaluation results that highlight the effect of the above are presented, and some hardware design examples are also given. >

Simulation and implementation of US QAM-based HDTV channel decoder

In this paper, we study different modulation techniques for visible light communication (VLC), taking illumination constraints into account. Two modulation schemes are compared, namely pulse amplitude modulation (PAM) and carrierless amplitude and phase (CAP) modulation, through both simulations and experimental measurements. The data link under study is based on low-cost components comprising a white light-emitting diode (LED) and a silicon PIN photodiode. Moreover, the proposed VLC system complies with illumination standards and limits the brightness level to that of a typical office room. The impact of the roll-off factor parameter, which is directly related to the total occupied bandwidth, and the maximum achievable throughput for PAM and CAP are studied. Moreover, adaptive postdistortion based on a Volterra series expansion is implemented to mitigate the effects of LED nonlinearity in practice. We also demonstrate that 8-PAM can outperform 64-CAP and discrete multitone (DMT) when the LED nonlinearity is adequately compensated.

Experimental Comparison of PAM and CAP Modulation for Visible Light Communication Under Illumination Constraints

In a previous work, a two-layer linear receiver was proposed as a low-complexity scheme that can achieve a good trade-off between performance and complexity in a massive multiple-input multiple-output (MIMO) context. For this scheme, the antenna array is split up into a number of subsets and multi-cell minimum mean-square-error (M-MMSE) combining is applied in each subset at the first layer. Then, the resulting outputs are combined using maximal-ratio combining (MRC) at the second layer. This paper presents a more complete performance analysis. First, we provide an entirely analytical derivation of the distribution of the output signal-to-noise-and-interference ratio (SINR) of first-layer processing based on multivariate statistical theory. The analysis includes both cases where the subset size is smaller or greater than the total number of signals. Furthermore, upper bounds and approximations on the average uplink SINR and achievable rate are derived. Numerical simulations confirm our analysis results. 

Uplink SINR and rate analysis in massive MIMO systems with two-layer linear receiver

An investigation of MIMO (multiple-input multiple-output) modulation techniques is presented in the context of a short-range Visible Light Communication (VLC) link compatible with the lighting function of common LED-based luminaires. A 2×2 VLC test bench was constructed based on typical low-cost components (white LEDs and photodiodes) and the use of an imaging lens to separate the transmitted streams at the receiver. Two transmission schemes are compared, both based on pulse amplitude modulation (PAM): spatial modulation (SM) and spatial multiplexing (SMP). BER performance is assessed through simulation based on channel characteristics measured on the test bench for both perfect alignment and laterally offset (misaligned) geometries. SMP is found to yield superior BER performance at the same spectral efficiency.

S. Roy

Papers

Simulation and implementation of US QAM-based HDTV channel decoder

Experimental Comparison of PAM and CAP Modulation for Visible Light Communication Under Illumination Constraints

Uplink SINR and rate analysis in massive MIMO systems with two-layer linear receiver

MIMO Techniques in a Visible Light Communication (VLC) Link with Imager