Prior to setting forth a short discussion of the related art, it may be helpful to set forth definitions of certain terms that will be used hereinafter. Many of these terms are defined in the 802.11 specification but it should be appreciated that the invention is not limited to systems and methods complying with the 802.11 specification.
The term “AP” is an acronym for Access Point(s) and is used herein to define a wireless fidelity “WiFi” or other wireless station that is an attachment point for user equipment “UE”.
The term “co-located” is used in herein to describe access points and refers to access points that are situated at the same general location, such as is the case with a multi-beam access point system, or to access points whose beams are sufficiently close or overlapping that one station is able to receive transmitted data from both or all of them. Access points may be implemented in software and therefore it is possible for multiple access points to be located at the same computing device which is running software to implement multiple access points.
The term “UE” is an acronym for User Equipment(s) and is used herein to define the station, e.g. WiFi station (STA) that attaches to an AP.
The term Station is a term used for any device which is a participant on the network, for example as used in the 802.11 specification. Both UEs and APs are considered in this context to be “Stations”.
Distributed Inter-Frame Space “DIFS” and Short Inter-Frame Space “SIFS” are types of Inter-Frame Space as defined in the 802.11 specifications.
The term MBAP is an acronym for MultiBeam Access Point and is usually used in the context of a MBAP system. This is an AP system that includes multiple APs which may operate simultaneously on the same radio channel where directive beams and other technology enable co-location of APs.
The term “beamformer” as used herein refers to analog and/or digital circuitry that implements beamforming and may include combiners and phase shifters or delays and in some cases amplifiers and/or attenuators to adjust the weights of signals to or from each antenna in an antenna array. Digital beamformers may be implemented in digital circuitry such as a digital signal processor (DSP), field-programmable gate array (FPGA), microprocessor or the central processing unit “CPU” of a computer to set the weights as may be expressed by phases and/or amplitudes of the above signals. Various techniques are used to implement beamforming including: Butler matrices, Blass Matrices and Rotman Lenses. In general, most approaches attempt to provide simultaneous coverage within a sector using multiple beams.
The term “cell” is used herein to refer to the area or region covered by a beam corresponding to an access point.
The specific Carrier Sense Multiple Access/Channel Assessment “CSMA/CA” mechanism used in the 802.11 media access code “MAC” is referred to as the distributed coordination function (DCF). A station that wishes to transmit first performs a clear channel assessment (CCA) by sensing the medium for a fixed duration, the DCF inter-frame space (DIFS).
The term Clear Channel Assessment (CCA) as used herein refers to a CCA function for example as defined in the 802.11 specifications;
The term Base Band Processor (BBP) as used herein may refer to encoding data and decoding data, for example so as to create the required WiFi baseband signal for any versions of the 802.11 protocol(s).
The term enhanced distributed channel access (EDCA) may refer for example to an extension of the basic DCF introduced in the 802.11e amendment to support prioritized quality of service (QoS). The EDCA mechanism defines four access categories (ACs).
The term AC is an acronym for access category as used herein may refer to AC as defined in the 802.11 specifications. Each AC may have specific values of access parameters, e.g., contention window minimum or maximum “CWmin”, or “CWmax”, Arbitration Inter-Frame Space Number “AIFSN” and transmission opportunity “TXOP” limit.
The term CW is an acronym for Contention window for example as defined in the 802.11 specifications. In the specifications a random backoff count is selected from the range [0, CW], where CW is typically equal to CWmin.
The term AIFS is an acronym for arbitration inter-frame space, for example as defined in the 802.11 specifications.
The term Transmit opportunity (TXOP) is a bounded period during which a station may transfer data of particular traffic, for example as defined in the 802.11 specifications.
WiFi has been implemented with a limited amount of frequency resources that use techniques of collision avoidance to allow multiple user equipments (UEs) to share the same channel. As the numbers of UEs proliferate, the impact of such a scheme restricts the ability of co-located Wi-Fi access points (APs) to support an ever increasing number of users.