On Non-coherent MIMO Channels in the Wideband Regime: Capacity and Reliability

We consider a multiple-input, multiple-output (MIMO) wideband Rayleigh block fading channel where the channel state is unknown to both the transmitter and the receiver and there is only an average power constraint on the input. We compute the capacity and analyze its dependence on coherence length, number of antennas and receive signal-to-noise ratio (SNR) per degree of freedom. We establish conditions on the coherence length and number of antennas for the non-coherent channel to have a "near coherent" performance in the wideband regime. We also propose a signaling scheme that is near-capacity achieving in this regime. We compute the error probability for this wideband non-coherent MIMO channel and study its dependence on SNR, number of transmit and receive antennas and coherence length. We show that error probability decays inversely with coherence length and exponentially with the product of the number of transmit and receive antennas. Moreover, channel outage dominates error probability in the wideband regime. We also show that the critical as well as cut-off rates are much smaller than channel capacity in this regime

DATA BATCHING FOR REDUCTION OF TRANSMISSION BURSTS

A method for reducing power consumption and thermals of a network interface card by batching network traffic is disclosed. An aspect of the subject technology may include receiving a first control signal, closing a gate corresponding to a buffer in response to the first control signal, receiving one or more data packets with the buffer, receiving a second control signal, opening the gate corresponding to the buffer in response to the second control signal, and transferring one or more data packets of the buffer for transmission in response to the gate opening

Time Deadline For Modem Mitigation Actions In Regards To Thermal Mitigation

This publication describes techniques for dynamic mitigation actions performed by a modem in response to a thermal situation. Dynamic mitigation actions can be completed by a modem after it receives a deadline time calculated by a caller (e.g., Application Programming Interface (API)) of the modem based on the thermal situation. The deadline time will represent how long the modem has to fully complete one or more mitigation action(s). The modem can decide the mitigation action timeline based off of the deadline time to allow for a better user experience. For example, if it is determined that the thermal situation is less critical (e.g., the temperature is increasing very slowly), a longer deadline time can be communicated from the API to allow the modem to slowly mitigate processes executing on the device. If it is determined that the thermal situation is more critical, the mitigation can be more aggressive with a shorter deadline time

Throttling downlink throughput to mitigate device temperature increase

The temperature of a mobile device can increase due to heavy use, e.g., high-speed downloads, large computational load, etc. Sustained periods of high temperature can damage the mobile device. The techniques of this disclosure reduce downlink throughput upon detection of device temperature that exceeds a threshold. Throughput is reduced, e.g., by signaling the thermal state to the network, by reporting lower channel quality indicator (CQI) values to the network, etc. After the temperature drops to a safe level, throughput is brought back up in a phased manner

Aggressive Smartphone Thermal Mitigation at High Temperatures

Thermal mitigation at a smartphone is improved by employing an emergency disconnect mode that is entered in response to heat at the smartphone exceeding a specified threshold. In the emergency disconnect mode, the smartphone is disconnected from a cellular network. This allows the components of a radio front-end of the smartphone to be turned off or placed in a low power mode while the smartphone is in the emergency disconnect mode, thereby rapidly decreasing the amount of heat generated at the device and allowing the smartphone to return to a normal mode of operation more quickly

Thermal Downlink Throttle UE Specific Approach

During operation, temperatures of a mobile communication device of an end user (user equipment or “UE”) can increase to high levels. In particular, UE temperatures can rise when receiving large amounts of data during downlink communication with a network. Generally, there is no ability to limit the amount of downlink throughput when the UE device is in single carrier mode. However, downlink throughput throttling can be used to thermally mitigate increasing UE temperatures. As the temperature of the UE increases, the network can be notified to decrease the amount of downlink throughput, thus reducing the power levels and the temperature of the UE. Once the temperature of the UE starts to reduce, the network can then be notified to increase downlink throughput in a gradual manner

Thermal Mitigation at User Equipment Based on Ambient Temperature

User equipment (UE) or other user devices employ thermal mitigation schemes that are responsive to the ambient temperature of the device. Such schemes can employ different levels or modes of thermal mitigation techniques based on ambient temperature, the thresholds that trigger the switch between levels or modes may be scaled based on ambient temperature, or a combination thereof

Multiple access networks over finite fields : optimality of separation, randomness and linearity

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (leaves 93-95).This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.We consider a time-slotted multiple access noisy as well as noise-free channel in which the received, transmit and noise alphabets belong to a finite field. We show that source-channel separation holds when the additive noise is independent of inputs. However, for input-dependent noise, separation may not hold. For channels over the binary field, we derive the expression for the probability of source-channel separation failing. We compute this probability to be 1/4 when the noise parameters are picked independently and uniformly. For binary channels, we derive an upper bound of 0.0776 bit for the maximum loss in sum rate due to separate source-channel coding when separation fails. We prove that the bound is very tight by showing that it is accurate to the second decimal place. We derive the capacity region and the maximum code rate for the noisy as well as noise-free channel where, code rate is defined as the ratio of the information symbols recovered at the receiver to the symbols sent by the transmitters in a slot duration. Code rate measures the overhead in transmitting in a slot under multiple access interference. We show for both noisy and noise-free channels that capacity grows logarithmically with the size of the field but the code rate is invariant with field size. For the noise-free channel, codes achieve maximum code rate if and only if they achieve capacity and add no redundancy to the shorter of the two information codewords. For the noise-free multiple access channel, we consider the cases when both transmitters always transmit in a slot, as well as when each transmitter transmits in a bursty fashion according to a Bernoulli process. For the case when both transmitters always transmit, we propose a systematic code construction and show that it achieves the maximum code rate and capacity. We also propose a systematic random code construction and show that it achieves the maximum code rate and capacity with probability tending to 1 exponentially with codeword length and field size. This is a strong coding theorem for this channel. For the case when transmitters transmit according to a Bernoulli process, we propose a coding scheme to maximize the expected code rate. We show that maximum code rate is achieved by adding redundancy at the less bursty transmitter and not adding any redundancy at the more bursty transmitter. For the noisy channel, we obtain the error exponents and hence, the expression for average probability of error when a random code is used for communicating over the channel.by Siddharth Ray.S.M

Energy efficient multiple antenna communication

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (leaves 111-115).We consider a multiple-input, multiple-output (MIMO) wideband Rayleigh block fading channel where the channel state is unknown at the transmitter and receiver and there is only an average input power constraint. We compute the capacity and analyze its dependence on coherence length, number of antennas and receive signal-to-noise ratio (SNR) per degree of freedom. We establish conditions on the coherence length and number of antennas for the non-coherent channel to have a "near coherent" performance in the wideband regime. We also propose a signaling scheme that is near-capacity achieving in this regime. We compute the decoding error probability and study its dependence on SNR, number of antennas and coherence length. We show that error probability decays inversely with coherence length and exponentially with the product of the number of transmit and receive antennas. Moreover, in the wideband regime, channel outage dominates error probability and the critical and cut-off rates are much smaller than channel capacity. In the second part of this thesis, we introduce the concept of a fiber aided wireless network architecture (FAWNA), which allows high-speed mobile connectivity by leveraging the speed of optical networks.(cont.) Specifically, we consider a single-input, multiple-output (SIMO) FAWNA, which consists of a SIMO wireless channel interfaced with an optical fiber channel through wireless-optical interfaces. We propose a design where the received wireless signal at each interface is sampled and quantized before being sent over the fiber. The capacity of our scheme approaches the capacity of the architecture, exponentially with fiber capacity. We also show that for a given fiber capacity, there is an optimal operating wireless bandwidth and number of interfaces. We show that the optimal way to divide the fiber capacity among the interfaces is to ensure that each interface gets enough rate so that its noise is dominated by front end noise rather than by quantizer distortion. We also show that rather than dynamically change rate allocation based on channel state, a less complex, fixed rate allocation scheme can be adopted with very small loss in performance.by Siddharth Ray.Ph.D