Robert A. DiFazio

Full duplex cellular systems: will doubling interference prevent doubling capacity?

Recent advances in antenna and RF circuit design have greatly reduced the crosstalk between the transmitter and receiver circuits on a wireless device, which enable radios to transmit and receive on the same frequency at the same time. Such a full duplex radio has the potential to double the spectral efficiency of a point-to-point radio link. However, the application of such a radio in current cellular systems (3GPP LTE) has not been comprehensively analyzed. This article addresses the fundamental challenges in incorporating full duplex radios in a cellular network to unlock the full potential of full duplex communications. We observe that without carefully planning, full duplex transmission might cause much higher interference in both uplink and downlink, which greatly limits the potential gains. Another challenge is that standard scheduling methods which attempt to achieve the maximum capacity gain lead to a severe loss in energy efficiency. In this article, we identify new tradeoffs in designing full duplex enabled radio networks, and discuss favorable conditions to operate in full duplex mode. New scheduling algorithms and advanced interference cancellation techniques are discussed, which are essential to maximize the capacity gain and energy efficiency. Under this new design, most of the gain is achievable with full duplex enabled base stations, while user equipment still operates in half duplex mode.

Improving small cell capacity with common-carrier full duplex radios

Recent progress in establishing the capability of radios to operate in full duplex mode on a single channel has been attracting growing attention from many researchers. We extend this work by considering the application to small cells, in particular resource-managed cellular systems similar to the TDD variant of LTE. We derive conditions where full duplex operation provides improved throughput compared to half duplex for a single cell scenario. We present a hybrid scheduler that defaults to half duplex operation but can assign full duplex timeslots when it is advantageous to do so. We compare the performance of such a scheduler with a traditional half duplex scheduler in terms of throughput and energy efficiency. Our simulation results show that we achieve as much as 81% of the capacity doubling promised by full duplex, with limitations deriving from interference effects specific to full duplex operation.

A low bias algorithm to estimate negative SNRs in an AWGN channel

Signal-to-noise ratio (SNR) is an important parameter in many receivers. In this letter, we derive a maximum-likelihood estimate of the amplitude of a binary phase-shift keying modulated signal and develop an iterative SNR search algorithm. Low bias is achieved for low SNR.

The bandwidth crunch: Can wireless technology meet the skyrocketing demand for mobile data?

Predictions abound on the growth of mobile data traffic driven by smart phones and tablet PCs that come with an expectation of broadband Internet connectivity everywhere and a demand for high quality video. The FCCs National Broadband Plan indicated that mobile data traffic in North America would increase by roughly 20 to 45 times between 2009 and 2014, and current data suggests these numbers may be exceeded. This paper examines how wireless technology can address the bandwidth challenge. We consider not only the track of cellular technology, but new approaches that promise improved spectral efficiency, use new spectrum, and rely on new network architectures. We recap cellular evolution from second generation through LTE-Advanced, address enhancements such as Coordinated Multipoint Transmission (CoMP) and examine other innovative multi-cell technology. More ambitious changes to cellular architecture such as relay nodes and terminal-to-terminal communications are discussed. Pico-cells, femto-cells, and forward-looking dense deployments are presented as promising approaches. New spectrum, including the use of TV white space is considered. We provide a quantitative assessment -perhaps a goal or perhaps another prediction - of what can be achieved.

New results on SNR estimation of MPSK modulated signals

Signal-to-noise ratio (SNR) is an important parameter in many receivers. In a previous letter B Li et al., (2002) we derived a maximum-likelihood amplitude estimator and obtained a low bias SNR estimation algorithm for a binary phase-shift keying (BPSK) modulated signal. We now extend the result and obtain a low bias SNR estimator for multiple phase-shift keying (MPSK) modulation. We compare our algorithm with others, such as a decision-directed approach. Simulations show that the new algorithm provides not only much lower bias and but also much smaller mean square error (MSE).

Dynamic Performance of a Chip Level Adaptive Equalizer in a UMTS High Speed Downlink Packet Access (HSDPA) Terminal

The HSDPA mode of the 3GPP UMTS FDD standard extends the peak downlink rate of the W-CDMA waveform to 14 Mbps. To achieve high rates across a multipath channel the demodulator must include an advanced receiver rather than a conventional Rake. This paper presents the performance of an NLMS-based adaptive equalizer that supports mobile velocities as high as 250 km/h. The equalizer works with radio and implementation impairments typical of a non-HSDPA receiver, so redesign of the terminal front end is not required. A key aspect of the design is dynamically adjusting the equalizer step size and leakage parameter. There is often concern about the ability of an adaptive algorithm to operate in a highly mobile environment. The transient behavior is discussed in the context of HSDPA operation and examples are provided of initial convergence and operation after a sudden change in propagation conditions.

Enhanced data detection employing compressed sensing In wireless communications

A framework and algorithm employing compressed sensing (CS) for orthogonal frequency division multiplexing (OFDM) systems is proposed. A compressive iterative interference cancellation for OFDM signal is presented. Prior knowledge of communication system is exploited to enhance data detection performance. Simulation results indicate that such an advanced data detection and receiver yields significant gains in bit error rate (BER) at low sampling rates.