Physical transceiver implementations for multiple-input multiple-output (MIMO) wireless communication systems suffer from transmit-RF (Tx-RF) impairments. In this paper, we study the effect on channel capacity and error-rate performance of residual Tx-RF impairments that defy proper compensation. In particular, we demonstrate that such residual distortions severely degrade the performance of (near-)optimum MIMO detection algorithms. To mitigate this performance loss, we propose an efficient algorithm, which is based on an i.i.d. Gaussian model for the distortion caused by these impairments. In order to validate this model, we provide measurement results based on a 4-stream Tx-RF chain implementation for MIMO orthogonal frequency-division multiplexing (OFDM).

/pdf/mimo-transmission-with-residual-transmit-rf-impairments-1shk8j9zp6.pdf

MIMO transmission with residual transmit-RF impairments

MIMO Transmission with Residual Transmit-RF Impairments

WiFi interface is known to be a primary energy consumer in mobile devices, and idle listening (IL) is the dominant source of energy consumption in WiFi. Most existing protocols, such as the 802.11 power-saving mode (PSM), attempt to reduce the time spent in IL by sleep scheduling. However, through an extensive analysis of real-world traffic, we found more than 60 percent of energy is consumed in IL, even with PSM enabled. To remedy this problem, we propose Energy-Minimizing idle Listening (E-MiLi) that reduces the power consumption in IL, given that the time spent in IL has already been optimized by sleep scheduling. Observing that radio power consumption decreases proportionally to its clock rate, E-MiLi adaptively downclocks the radio during IL, and reverts to full clock rate when an incoming packet is detected or a packet has to be transmitted. E-MiLi incorporates sampling rate invariant detection, ensuring accurate packet detection and address filtering even when the receiver's sampling clock rate is much lower than the signal bandwidth. Further, it employs an opportunistic downclocking mechanism to optimize the efficiency of switching clock rate, based on a simple interface to existing MAC-layer scheduling protocols. We have implemented E-MiLi on the USRP software radio platform. Our experimental evaluation shows that E-MiLi can detect packets with close to 100 percent accuracy even with downclocking by a factor of 16. When integrated with 802.11, E-MiLi can reduce energy consumption by around 44 percent for 92 percent of users in real-world wireless networks.

/pdf/e-mili-energy-minimizing-idle-listening-in-wireless-networks-lq2aqjn82k.pdf

E-MiLi: Energy-Minimizing Idle Listening in Wireless Networks

WiFi interface is known to be a primary energy consumer in mobile devices, and idle listening (IL) is the dominant source of energy consumption in WiFi. Most existing protocols, such as the 802.11 power-saving mode (PSM), attempt to reduce the time spent in IL by sleep scheduling. However, through an extensive analysis of real-world traffic, we found more than 60% of energy is consumed in IL, even with PSM enabled. To remedy this problem, we propose E-MiLi (Energy-Minimizing idle Listening) that reduces the power consumption in IL, given that the time spent in IL has already been optimized by sleep scheduling. Observing that radio power consumption decreases proportionally to its clock-rate, E-MiLi adaptively downclocks the radio during IL, and reverts to full clock-rate when an incoming packet is detected or a packet has to be transmitted. E-MiLi incorporates sampling rate invariant detection, ensuring accurate packet detection and address filtering even when the receiver's sampling clock-rate is much lower than the signal bandwidth. Further, it employs an opportunistic downclocking mechanism to optimize the efficiency of switching clock-rate, based on a simple interface to existing MAC-layer scheduling protocols. We have implemented E-MiLi on the USRP software radio platform. Our experimental evaluation shows that E-MiLi can detect packets with close to 100% accuracy even with downclocking by a factor of 16. When integrated with 802.11, E-MiLi can reduce energy consumption by around 44% for 92% of users in real-world wireless networks.

/pdf/e-mili-energy-minimizing-idle-listening-in-wireless-networks-3wu7cpjygo.pdf

E-MiLi: energy-minimizing idle listening in wireless networks

Antenna arrays have been demonstrated as a very promising technique for high-speed wireless networks, and are anticipated to be indispensable components in future wireless communication systems. This review paper presents an overview of the circuit techniques on combining signals from different receive array elements as well as splitting signals to different transmit array elements with emphasis on silicon-based solutions. It also reviews circuit techniques to control the phase and the amplitude of signals from/to each array element such that signals from those array elements can be combined and split in a desired manner for achieving high data rate communications as well as interference management.

/pdf/supporting-and-enabling-circuits-for-antenna-arrays-in-45ksej910f.pdf

Supporting and Enabling Circuits for Antenna Arrays in Wireless Communications

An 802.11n-draft-compliant 2times2, 2-stream MIMO radio SoC, incorporating two dual-band RF transceivers, analog baseband filters, data converters, digital PHY and MAC, and a PCI Express interface, has been integrated in a standard 0.13- mum digital CMOS technology with a die area of 36 mm2. The receiver achieves noise figures of 4 dB and 6 dB, respectively, at 2.4 GHz and 5 GHz. The transmitter EVM for a 2-stream, 40-MHz-bandwidth 64-QAM OFDM signal is - 31 dBc at 2.4 GHz and -8 dBm output power and -31.5 dBc at 5 GHz and - 4 dBm output power.

A Dual-Band CMOS MIMO Radio SoC for IEEE 802.11n Wireless LAN

Wireless local area networks based on the IEEE 802.11 standard are rapidly replacing wires within homes and offices. The latest data-rate amendment to the IEEE 802.11 standard, known as the 802.11n, provides enhanced user experience by exploiting MIMO techniques that use multiple antennas for both transmitter and receiver. In conjunction with MAC layer improvements such as aggregating data, the 802.11n standard supports PHY data rates as high as 600 Mb/s with four spatial streams. This article discusses various MAC and PHY level modifications introduced in 802.11n, as well as the architecture, design trade-offs, and implementation details of a two spatial stream CMOS 802.11n-draft-compliant SoC.

S.-W.M. Chen

Papers

A Dual-Band CMOS MIMO Radio SoC for IEEE 802.11n Wireless LAN

Design and implementation of a CMO 802.11n SoC