Multiplex communications – Communication over free space – Combining or distributing information via time channels
Reexamination Certificate
1996-02-01
2001-08-28
Nguyen, Chau (Department: 2663)
Multiplex communications
Communication over free space
Combining or distributing information via time channels
C370S395430
Reexamination Certificate
active
06282187
ABSTRACT:
BACKGROUND OF THE INVENTION
The recent allocation of frequencies by the FCC at 2.5 GHz and 28 GHz has enabled the delivery of broadband-ISDN services to residential and commercial users through wireless means. Broadband ISDN typically uses ATM as the link layer of the network protocol. ATM is a switch-oriented link protocol where each user has a dedicated connection to the switch and the switch manages bandwidth contention by multiple users by queues input cells until they can be delivered to the appropriate output. In a wireless point to multipoint system, the analog of the switch resides in a base station, and the link to the switch is a shared medium by all users whose access to that medium must be controlled. Therefore, for wireless point to multipoint systems there is the additional need for medium access control which is not required in ordinary ATM networks.
The medium access control requirements for wireless point to multipoint systems where the users are stationary are unique compared to other wireless networks such as wireless local area networks (LANs) as specified by the IEEE 802.11 standard. A wireless point to multipoint system can take advantage of the stationary nature of users enabling the use of highly directional antennas at the user stations. However, the base station will still employ broad beam antennas and will thus have multiple user transmissions received simultaneously. Medium access control will be necessary to ensure that mutual interference by multiple user transmission impinging on the base station antenna is eliminated.
There are numerous MAC protocols in currently in use by both wired and wireless standards. In Ethernet, where the cabling is a shared medium, carrier-sense multiple access is employed, which is essentially a listen before talk approach. In wireless LANs, such as that specified by the IEEE 802.11 standard, medium access control is also managed through carrier-sense multiple access. This is possible because portable user terminals will each typically have all omnidirectional antenna so that each user terminal can receive a transmissions from other users and ascertain whether the frequency channel is available. This is not possible with wireless point to multipoint systems where stationary users employ directional antennas, as they cannot receive transmissions from other users.
An additional complication in wide area wireless point to multipoint systems, is that the two way range differential between users close to the base station and those distant to the base station can be much larger than a modulation symbol.
The impetus for the invention is therefore to develop a networking protocol which provides bandwidth to users on an on-demand basis, which controls access by users to the shared wireless medium, which is bandwidth efficient, and which can be implemented with the minimum of hardware cost.
DESCRIPTION
SUMMARY OF THE INVENTION
A networking protocol for wireless point (base station) to multipoint (user) networks where the users are stationary which utilizes time-division multiplexing the in the direction of the base station to the user, heretofore called the downstream direction, and time-division multiple access in the direction of the user to the base station, heretofore called the upstream direction, where medium access control actively assigns time slots in the upstream direction to accommodate varying demands for bandwidth by multiple users, where upstream frame timing is synchronized to the downstream frame timing, where time slots carry individual ATM cells, where the first time slot of the downstream frame carries a frame start ATM cell, where upstream time slot synchronization is maintained to within +2 modulation symbols through timing control from the base station to the user, where random access time slots are used for control plane requests by users entering the network and users in standby mode seeking to begin a session, where polling is used for management plane functions and responses by users are on a polling response time slot.
SPECIFIC FEATURES OF THE INVENTION
A networking protocol for wireless point (based station) to multipoint (user) networks with stationary users utilizing high gain directional antennas where:
1. Means for transmission convergence layer is provided through
a) Time-division multiplexing is utilized in the direction of the base station to the user, heretofore called the downstream direction;
b) Time-division multiple access is used in the direction of the user to the base station, heretofore called the upstream direction;
c) Time slots in the upstream direction have two preamble bytes, one ATM cell, and a one byte guard band;
d) Time slots in the downstream direction have one sync byte, one ATM cell, and no guard band;
e) Upstream frame timing is synchronized to the downstream frame timing, where the first time slot of the downstream frame carries a frame start ATM cell which is defined by a unique reserved VPI/VCI;
f) Frame periods in both the upstream and downstream directions are approximately but not greater than six milliseconds in length to allow delivery of voice traffic with minimum latency.
2. Means for physical medium dependent layer where
a) The downstream is continuous-carrier, without pulse shape filtering, with frequency channels symbol synchronous and spaced 1/T
D
apart where T
D
is the period of a downstream modulation symbol;
b) The upstream is burst-mode with 25% excess bandwidth root raised cosine filtered with frequency channels spaced 1.25 T
U
apart where T
U
is the period of an upstream modulation symbol.
c) QPSK or alternately 16 QAM modulation is employed on the upstream and the downstream.
d) A concatenated (60), 54) Reed-Solomon over GF(256) and rate 7/8 convolutional code is used on the downstream; and
e) A (59, 53) Reed-Solomon code over GF(256) is used on the upstream.
3. Means for control plane functions is provided through
a) In-band signaling through ATM cells with reserved VIP/VCIs so that the requirements for acquisition, demodulation, and forward error correction are uniform across the data, control, and management planes of the network protocol;
b) Transmission convergence layer medium access control which dynamically assigns the time slots in the upstream direction to accommodate varying demands for bandwidth by multiple users;
c) Contiguous time slots at the beginning of the upstream frame are used for entry into the network by users whose two-way range timing has not been resolved to avoid mutual interference, where users entering the network remain on the net entry time slots until their timing is aligned by means described in claim
1
;
d) Session requests are performed on a contention basis through contention time slots;
e) Carrying control plane acknowledgment of service requests in the payload of the frame start ATM cell in the downstream frame.
4. Means for management plane functions are provided through
a) In-band signaling through ATM cells with reserved VPI/VCIs so that the requirements for acquisition, demodulation, and forward error correction are uniform across the data, control, and management planes of the network protocol;
b) Polling users by the base station, with uses responding on dedicated time slots in the upstream frame;
c) Carrying management plane polling requests in the payload of the frame start ATM cell in the downstream frame carries.
d) Upstream time slot synchronization is maintained to within ±2 modulation symbols through timing control from the base station to the user and through slaving the user transmit symbol clock to its received symbol clock in the transmission convergence layer.
e) Upstream power control is employed to ensure adequate received signal strength at the base station while minimizing adjacent cell interference.
5. Hardware and software means for implementing above claims in the base station including:
a) means for routing of in-band signaling ATM cells by the ATM switching device to and from the central processing unit;
b) means for measuring timing offsets by subscribers through count
Evans Allan
Hunter April
VanBlaricom Charles
Lee Chiho Andrew
Nguyen Chau
Stanford Telecommunications, Inc.
Zegeer Zim
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