The demand for spectrum will continue to increase in the next years. The 13 GHz band (12.7-13.25 GHz) could be considered as a future candidate for unlicensed use due to its allocation to the same types of incumbents as the recently opened 6 GHz band. This paper studies the feasibility of spectrum sharing in the 13 GHz band through simulations of aggregate interference from Radio Local Area Networks (RLAN), specifically Wi-Fi devices, to fixed and mobile terrestrial links and Geostationary (GSO) and Non-GSO satellite incumbents. The simulations are based on novel aggregate interference models that incorporate space, time, and frequency-domain considerations in different scenarios and using real data. The results show that coexistence is possible and this analysis can be replicated in other regions and bands.

The 6 GHz band is currently being proposed to open for unlicensed use in different countries. In the United States, the Federal Communications Commission (FCC) just made available 1200 MHz of spectrum, from 5925 to 7125 MHz, for Radio Local Access Networks (RLANs) on April 23rd, 2020. This band is currently allocated to Fixed Service (FS), Mobile Service (MS), and Fixed Satellite Service (FSS) links. The purpose of this paper is to analyze the impact of aggregate interference from RLANs in the United States to FSS links in this band considering the rules recently proposed by the FCC. This work includes a sensitivity analysis of the main parameters that are currently under discussion among incumbents and Wi-Fi advocates. One of these parameters is the Wi-Fi airtime utilization, which is estimated in this work by measuring the airtime utilization using a software-defined radio in different environments. We found that coexistence will always be possible for low-power indoor access points (APs) and standard-power outdoor APs, which may generate aggregate interference up to -25.1 dB interference to noise ratio (I/N). This analysis provides useful guidelines to study the implications of spectrum sharing between RLANs and FSS in this band and can be replicated to other regions of the world.

We show that a differentially encoded maximal-length shift register sequence (or M-sequence) is also an M-sequence or the logical complement of an M-sequence. The differentially encoded sequence is a cyclically shifted version of the original M-sequence or its complement.

A code construction for a T active users out of N multiple-access system (TANMAS) is discussed. The multiple-access channel (MAC) that is used in the TANMAS is a discrete-time noiseless real adder channel used without feedback with N real or binary inputs. Each input may be affected by an unknown, slowly varying channel gain and by an unknown, slowly varying channel offset. A set of N codes is constructed such that the sum of codewords of any known set of T or less active users is uniquely decodable. The sum rate of the codes approaches one from above if the input alphabet of the MAC is binary, and it approaches one from below if the input symbols are real numbers. For the case when the set of active users is unknown. For the case when the set of active users is unknown, it is shown that this set can be identified uniquely (in addition to unique decodability) provided that at most T/2 users are active simultaneously. The sum rate is then reduced to 1/2, which is approached from above and from below, respectively, for binary and for real channel inputs. A simple decoding algorithm which operates over the reals is given for the case when the set of active users is known. It is pointed out that one of the applications of the given codes is in hybrid multiple-access systems that use both multiple-access coding and collision resolution.>

Random-access systems (RAS) for collision-type channels have been studied extensively under the assumption of an infinite population which generates a Poisson arrival process. If the population is finite and if the (practically desirable) free-access channel-access protocol is used, then it is shown that the specification of a channel-exit protocol is crucial for the stability and the fairness of the RAS. Free-exit and blocked-exit protocols are analyzed and it is concluded that the p-persistent blocked-exit protocol provides the mechanisms to assure stability and fairness for a wide range of arrival process models.

A model is proposed for the situation whereMusers share a common communication resource but, because of unknown time offsets among their clocks, cannot transmit their data packets in a time-sharing mode and, because of the lack of a feedback link, can never determine these time offsets and also can never be sure of the outcomes of their individual packet transmissions. Each user is required to make his packet transmissions at times determined by a protocol signal that is independent of the data to be sent. The capacity and zero-error capacity regions of this channel are determined for both the unsynchronized and slot-synchronized cases; these four regions are shown to coincide. It is further shown that a dense set of rate points on the outer boundary of this region can be achieved in the slot-synchronized case. Specific constructions of protocol sequences for achieving these points are given, and the technique of "decimation decoding" is introduced for identifying the sender of each successfully transmitted packet. Maximum-erasure burst-correcting codes over an alphabet of arbitrary size are constructed and shown to suffice for reconstructing the packets lost in "collisions" when these protocol sequences are used.

The throughput characteristics of contention-based random-access systems (RAS's) which useQ-ary tree algorithms (whereQ \geq 2is the number of groups into which contending users are split) of the Capetanakis-Tsybakov-Mikhailov-Vvedenskaya type are analyzed for an infinite population of identical users generating packets according to a Poisson process. Both free and blocked channel-access protocols are considered in combination withQ-ary collision resolution algorithms that exploit either binary ("collision/no collision") or ternary ("collision/ success / idle") feedback. For the resulting RAS's, functional equations for transformed generating functions of the first two moments of the collision resolution interval length are obtained and solved. The maximum stable throughput as a function ofQis given. The results of a packet-delay analysis are also given, and the analyzed RAS's are compared among themselves and with the slotted ALOHA system in terms of both system throughput and packet delay. It is concluded that the "practical optimum" RAS (in terms of ease of implementation combined with good performance) uses free (i.e., immediate) channel access and ternary splitting (i.e.,Q = 3) with binary feedback.