Everest W. Huang

Asymmetric multilevel outphasing architecture for multi-standard transmitters

We describe a new outphasing transmitter architecture in which the supply voltage for each PA can switch among multiple levels. It is based on a new asymmetric multilevel outphasing (AMO) modulation technique which increases overall efficiency over a much wider output power range than the standard LINC system while maintaining high linearity. For demonstration, the overall transmitter is simulated in a 65nm CMOS process with HSUPA and WLAN signals. The simulation results show an efficiency improvement from 17.7% to 40.7% for HSUPA at 25.3dBm output power and from 11.3% to 35.5% for WLAN 802.11g at 22.8dBm while still meeting system linearity requirements.

Integrated transceiver arrays for multiple antenna systems

In this paper, we present area-efficient multiple antenna transceiver front ends. A portion of the greatly increased capacity (compared to a single antenna system) of the multiple antenna system is traded off for relaxed circuit noise requirements. This allows circuits without physically large on-chip inductors to be used, resulting in significant chip area savings. Comparing the area and noise performance between a narrowband low noise amplifier (LNA) and a broadband LNA shows a simulated 3 dB increase in noise figure but a threefold decrease in area. Furthermore, multiple receiver front ends for a proposed four transmit, four receive antenna (4/spl times/4) system have a smaller area than some reported single front ends.

Packet Acquisition Performance of Frequency-Hop Spread-Spectrum Systems in Partial-Band Interference

For a frequency-hop (FH) spread-spectrum communication system, the packet error rate is dependent on both the performance of the error-correcting code and the ability of the receiver to detect and acquire timing of incoming packets. The performance of coding in FH systems in the presence of partial-band interference has been well studied, and it has been shown that turbo codes can work well in partial-band jamming. If the noise and interference are sufficient, however, the receiver will likely fail to correctly acquire the packet due to loss of the synchronization symbols, thus increasing the packet error rate. In this paper, we analyze packet acquisition for FH systems in the presence of partial-band jamming and determine optimal acquisition techniques. Simpler, near-optimal acquisition methods are also considered. We further consider the impact of imperfect acquisition along with established results on turbo error-correcting coding for FH systems to examine the overall packet error probability for partial-band interference channels.

Peak to Average Power Reduction for Low-Power OFDM Systems

For orthogonal frequency-division multiplexing (OFDM) systems, peak to average power ratio (PAPR) can be a major impediment to efficient transmission due to the need to use inefficient highly linear amplifiers. This paper presents an iterative algorithm to reduce the PAPR of a low-power OFDM system by 3 dB at a clipping probability of 10-2, and over 5 dB for 10-5 with asymptotically no loss in code rate for low signal to noise ratios (SNR). The reduced PAPR allows the system to use a more efficient form of linear amplifier, for an overall reduction in transmitter power consumption by over a factor of three at low SNR. In addition, the algorithm does not require any side information to be transmitted to the receiver to allow decoding.

An approach for area- and power-efficient low-complexity implementation of multiple antenna transceivers

In this paper, signal-to-noise ratio (SNR) gain is used to resolve the limits of circuit chip area and power consumption in multiple antenna systems. Multiple antennas promise greatly increased capacity, but increase chip area and power consumption due to multiple RF front ends and additional resources to process multiple streams. However, trading capacity for diversity gain decreases the SNR required for similar data rates as a single antenna system. For analog circuits, the SNR gain relaxes noise requirements, making viable both inductorless and reduced power consumption circuits. For example, simulations of a inductorless low noise amplifier (LNA) show a 3 dB increase in noise figure but threefold decrease in area when compared with a conventional narrowband LNA. Similarly, a narrowband LNA has a slightly higher noise figure when operated at half its original power consumption. For digital circuits, the lowered complexity of high diversity systems decreases the size and power consumption of the digital processor.

Analysis and extension of zigzag multiuser detection

Simultaneous transmissions from different nodes in a network can result in multiuser interference in which an intended receiver hears the overlapping combination of two or more transmissions. In the case where there are multiple observations with different time offsets of a collision (e.g., if the packet retransmissions also collide, or if there is a cooperating receiver with different propagation delays to the transmitters), zigzag [1] decoding can be employed. In this paper, we analyze the performance of zigzag decoding for the case of two receiving nodes with two simultaneous transmitters in an additive white Gaussian noise (AWGN) channel. We also present a soft-decision version of zigzag decoding and show that it is the optimal MAP decision rule.

Cooperative interference cancellation for wireless networks

A typical military airborne networking scenario involves small groups of relatively closely-spaced aircraft which fly as a unit to perform a common mission. These aircraft need to maintain very long data links with other aircraft in the presence of strong interference from hostile jammers. Due to the physical separation of the aircraft, the time difference of arrival can often be greater than the chip rate of the desired signal, allowing multiple aircraft to perform interference cancellation to greatly increase their resistance to jamming. In this paper, the performance of a zigzag-like algorithm [1] is simulated and compared against single receiver performance in the presence of strong interference. Performance of these algorithms in the presence of strong interference is shown for both uncoded and coded transmissions, which effectively mitigate strong interference with only 0.5 dB of performance loss compared to the unjammed case regardless of the jammer strength.