68 research outputs found
Energy-Efficient Non-Orthogonal Transmission under Reliability and Finite Blocklength Constraints
This paper investigates an energy-efficient non-orthogonal transmission
design problem for two downlink receivers that have strict reliability and
finite blocklength (latency) constraints. The Shannon capacity formula widely
used in traditional designs needs the assumption of infinite blocklength and
thus is no longer appropriate. We adopt the newly finite blocklength coding
capacity formula for explicitly specifying the trade-off between reliability
and code blocklength. However, conventional successive interference
cancellation (SIC) may become infeasible due to heterogeneous blocklengths. We
thus consider several scenarios with different channel conditions and
with/without SIC. By carefully examining the problem structure, we present in
closed-form the optimal power and code blocklength for energy-efficient
transmissions. Simulation results provide interesting insights into conditions
for which non-orthogonal transmission is more energy efficient than the
orthogonal transmission such as TDMA.Comment: accepted by IEEE GlobeCom workshop on URLLC, 201
Downlink Transmission of Short Packets: Framing and Control Information Revisited
Cellular wireless systems rely on frame-based transmissions. The frame design
is conventionally based on heuristics, consisting of a frame header and a data
part. The frame header contains control information that provides pointers to
the messages within the data part. In this paper, we revisit the principles of
frame design and show the impact of the new design in scenarios that feature
short data packets which are central to various 5G and Internet of Things
applications. We treat framing for downlink transmission in an AWGN broadcast
channel with K users, where the sizes of the messages to the users are random
variables. Using approximations from finite blocklength information theory, we
establish a framework in which a message to a given user is not necessarily
encoded as a single packet, but may be grouped with the messages to other users
and benefit from the improved efficiency of longer codes. This requires changes
in the way control information is sent, and it requires that the users need to
spend power decoding other messages, thereby increasing the average power
consumption. We show that the common heuristic design is only one point on a
curve that represents the trade-off between latency and power consumption.Comment: 10 page
Short-Packet Downlink Transmission with Non-Orthogonal Multiple Access
This work introduces downlink non-orthogonal multiple access (NOMA) into
short-packet communications. NOMA has great potential to improve fairness and
spectral efficiency with respect to orthogonal multiple access (OMA) for
low-latency downlink transmission, thus making it attractive for the emerging
Internet of Things. We consider a two-user downlink NOMA system with finite
blocklength constraints, in which the transmission rates and power allocation
are optimized. To this end, we investigate the trade-off among the transmission
rate, decoding error probability, and the transmission latency measured in
blocklength. Then, a one-dimensional search algorithm is proposed to resolve
the challenges mainly due to the achievable rate affected by the finite
blocklength and the unguaranteed successive interference cancellation. We also
analyze the performance of OMA as a benchmark to fully demonstrate the benefit
of NOMA. Our simulation results show that NOMA significantly outperforms OMA in
terms of achieving a higher effective throughput subject to the same finite
blocklength constraint, or incurring a lower latency to achieve the same
effective throughput target. Interestingly, we further find that with the
finite blocklength, the advantage of NOMA relative to OMA is more prominent
when the effective throughput targets at the two users become more comparable.Comment: 15 pages, 9 figures. This is a longer version of a paper to appear in
IEEE Transactions on Wireless Communications. Citation Information: X. Sun,
S. Yan, N. Yang, Z. Ding, C. Shen, and Z. Zhong, "Short-Packet Downlink
Transmission with Non-Orthogonal Multiple Access," IEEE Trans. Wireless
Commun., accepted to appear [Online]
https://ieeexplore.ieee.org/document/8345745
- …