Toward Massive, Ultrareliable, and Low-Latency Wireless Communication With Short Packets

Abstract

Abstract-Most of the recent advances in the design of highspeed wireless systems are based on information-theoretic principles that demonstrate how to efficiently transmit long data packets. However, the upcoming wireless systems, notably the 5G system, will need to support novel traffic types that use short packets. For example, short packets represent the most common form of traffic generated by sensors and other devices involved in Machine-toMachine (M2M) communications. Furthermore, there are emerging applications in which small packets are expected to carry critical information that should be received with low latency and ultrahigh reliability.Current wireless systems are not designed to support shortpacket transmissions. For example, the design of current systems relies on the assumption that the metadata (control information) is of negligible size compared to the actual information payload. Hence, transmitting metadata using heuristic methods does not affect the overall system performance. However, when the packets are short, metadata may be of the same size as the payload, and the conventional methods to transmit it may be highly suboptimal.In this article, we review recent advances in information theory, which provide the theoretical principles that govern the transmission of short packets. We then apply these principles to three exemplary scenarios (the two-way channel, the downlink broadcast channel, and the uplink random access channel), thereby illustrating how the transmission of control information can be optimized when the packets are short. The insights brought by these examples suggest that new principles are needed for the design of wireless protocols supporting short packets. These principles will have a direct impact on the system design.

Finite-blocklength bounds on the maximum coding rate of rician fading channels with applications to pilot-assisted transmission

“…Classic informationtheoretic performance metrics such as ergodic and outage capacity, provide inaccurate benchmarks to the performance of short-packet coding schemes, because of their asymptotic nature [2], [3]. In particular, these performance metrics are unable to capture the tension between the throughput gains in the transmission over wireless fading channels attainable by exploiting channel diversity and the throughput losses caused by the insertion of pilot symbols, which are needed to estimate the wireless fading channel (pilot overhead).…”

“…Furthermore, let Y = HX + W where W is defined as in (2). The probability density function (pdf) of Y is given by…”

Convergence of Limited Communication Gradient Methods

“…where a i and b i are uniform random random variables on the interval [1,5]. The private constraint of machine i = 1, 2, 3, 4 is Q i = {(x, y) ∈ R 2 |x, y ≥ 0, x + y ≤ 3}.…”

“…, N . 5 We first show that ∇f (x), x−x > 0 for all x ∈ R N + \X . Consider first the case when x ∈ R N + \ X and x j > 0 for some j ∈ J .…”

“…Light communications are also essential in coordinating data networks [4], where the control channels that support the data channels are obviously allocated limited bandwidth. Another relevant example is within the emerging technology of extremely low latency networking or tactile internet [5], where information, especially for real time control applications, will be transmitted with very low latencies over wireless and wired networks. However, this comes at a cost of using short packets containing limited information.…”