9 research outputs found
A phase feedback based extended space-time block code for enhancement of diversity
In this paper we propose a generalization of extended orthogonal space-time block codes (EO-STBCs) for MIMO (multi-input/multi-output) channels using four transmit antennas for quasi-static flat fading channels. Since full rate and complex orthogonal space-time block codes (STBCs) do not exist for more than two transmit antennas, we propose a feedback based STBC scheme. In this scheme, phases of certain symbols are rotated according to the feedback from the receiver which is equivalent to rotating the phases of the corresponding channel coefficients. Simulation results show that this rotation phase feedback method achieves a satisfactory performance and outperforms the previous closed-loop space-time block codes, even when the feedback is quantized
Indoor off-body wireless communication: static beamforming versus space-time coding
The performance of beamforming versus space-time coding using a body-worn textile antenna array is experimentally evaluated for an indoor environment, where a walking rescue worker transmits data in the 2.45 GHz ISM band, relying on a vertical textile four-antenna array integrated into his garment. The two transmission scenarios considered are static beamforming at low-elevation angles and space-time code based transmit diversity. Signals are received by a base station equipped with a horizontal array of four dipole antennas providing spatial receive diversity through maximum-ratio combining. Signal-to-noise ratios, bit error rate characteristics, and signal correlation properties are assessed for both off-body transmission scenarios. Without receiver diversity, the performance of space-time coding is generally better. In case of fourth-order receiver diversity, beamforming is superior in line-of-sight conditions. For non-line-of-sight propagation, the space-time codes perform better as soon as bit error rates are low enough for a reliable data link
General Rank Multiuser Downlink Beamforming With Shaping Constraints Using Real-valued OSTBC
In this paper we consider optimal multiuser downlink beamforming in the
presence of a massive number of arbitrary quadratic shaping constraints. We
combine beamforming with full-rate high dimensional real-valued orthogonal
space time block coding (OSTBC) to increase the number of beamforming weight
vectors and associated degrees of freedom in the beamformer design. The
original multi-constraint beamforming problem is converted into a convex
optimization problem using semidefinite relaxation (SDR) which can be solved
efficiently. In contrast to conventional (rank-one) beamforming approaches in
which an optimal beamforming solution can be obtained only when the SDR
solution (after rank reduction) exhibits the rank-one property, in our approach
optimality is guaranteed when a rank of eight is not exceeded. We show that our
approach can incorporate up to 79 additional shaping constraints for which an
optimal beamforming solution is guaranteed as compared to a maximum of two
additional constraints that bound the conventional rank-one downlink
beamforming designs. Simulation results demonstrate the flexibility of our
proposed beamformer design
A Phase Feedback Based Extended Space-Time Block Code for Enhancement of Diversity
This is a conference paper [© IEEE]. It is also available at: http://ieeexplore.ieee.org/ Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.In this paper we propose a generalization of extended orthogonal space-time block codes (EO-STBCs) for MIMO (multi-input/multi-output) channels using four transmit antennas for quasi-static flat fading channels. Since full rate and complex orthogonal space-time block codes (STBCs) do not exist for more than two transmit antennas, we propose a feedback based STBC scheme. In this scheme, phases of certain symbols are rotated according to the feedback from the receiver which is equivalent to rotating the phases of the corresponding channel coefficients. Simulation results show that this rotation phase feedback method achieves a satisfactory performance and outperforms the previous closed-loop space-time block codes, even when the feedback is quantized
Interleaving Channel Estimation and Limited Feedback for Point-to-Point Systems with a Large Number of Transmit Antennas
We introduce and investigate the opportunities of multi-antenna communication
schemes whose training and feedback stages are interleaved and mutually
interacting. Specifically, unlike the traditional schemes where the transmitter
first trains all of its antennas at once and then receives a single feedback
message, we consider a scenario where the transmitter instead trains its
antennas one by one and receives feedback information immediately after
training each one of its antennas. The feedback message may ask the transmitter
to train another antenna; or, it may terminate the feedback/training phase and
provide the quantized codeword (e.g., a beamforming vector) to be utilized for
data transmission. As a specific application, we consider a multiple-input
single-output system with transmit antennas, a short-term power constraint
, and target data rate . We show that for any , the same outage
probability as a system with perfect transmitter and receiver channel state
information can be achieved with a feedback rate of bits per channel
state and via training transmit antennas on average, where and
are independent of , and depend only on and . In addition,
we design variable-rate quantizers for channel coefficients to further minimize
the feedback rate of our scheme.Comment: To appear in IEEE Transactions on Wireless Communication
MIMO and beamforming techniques for reliable off-body communication using textile antennas
Wireless communication systems with textile antennas can be entirely integrated into clothing or garment and do not hinder the user’s movements. Great interest in such an off-body communication system exists in the field of rescue operations, such as firefighting, where the automated communication of vital data between rescue workers or to a base station improves the coordination of the operation and the safety of the rescue workers. To set up a reliable wireless off-body communication link, a number of specific challenges need to be overcome. Persons equipped with wearable antennas constantly change position, orientation, walking pace and body posture. This results in unpredictably variable fading and shadowing on the received signals, producing bit errors, even in case of a high average received signal-to-noise ratio. Fading and shadowing hence dramatically limit the reliability of a communication system with single antennas at both link ends. Using multiple textile antennas, the performance degradation is drastically limited, by means of MIMO and/or beamforming techniques, which mitigate the signal variation and/or produce a higher average signal-to-noise ratio at the receiver, respectively.
The research documented in this PhD thesis includes multiple measurement campaigns and their analysis for a diverse number of off-body communication configurations, using MIMO and beamforming techniques with textile antennas.
Off-body MIMO techniques are shown to result in a significant improvement of the reliability of the communication, an improvement which further increases when more antennas are used. Channel variation typically of the off-body scenario is tracked with a computationally low-cost system, using adaptive digital low-pass filtering on decision-oriented channel estimation information. Off-body static beamforming techniques are shown to often outperform transmit diversity systems, producing a lower bit error rate at the receiver, provided that receiver diversity is employed to compensate for the channel variation. Finally, a new theoretical model specifically for the off-body MIMO communication channel is presented, allowing an accurate reproduction of bit error rate and channel capacity characteristics as well as the generation of measurement-like random off-body MIMO channel realizations for simulation purposes