Co-location negotiation scheme for wireless computer networks

Details Co-location negotiation scheme for wireless computer networks Co-location negotiation scheme for wireless computer networks

1999-04-15

2002-11-12

Chin, Wellington (Department: 2665)

Multiplex communications

Communication techniques for information carried in plural...

Adaptive

C370S280000, C370S337000, C370S458000, C455S450000, C455S452200

Reexamination Certificate

active

06480506

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to communications in a computer network and, in particular, to a scheme for accommodating multiple overlapping networks that share a common communication channel.
BACKGROUND
In the above-referenced co-pending application, Ser. No. 09/151,452, which is incorporated herein by reference, a computer network adapted for use in the home environment was described. That architecture included a number of network components arranged in a hierarchical fashion and communicatively coupled to one another through communication links operative at different levels of the hierarchy. At the highest level of the hierarchy, a communication protocol that supports dynamic addition of new network components at any level of the hierarchy according to bandwidth requirements within a communication channel operative at the highest level of the network hierarchy is used. Preferably, the communication channel is supported on a wireless communication link.
The generalization of this network structure is shown in
FIG. 1. A
subnet
10
includes a server
12
. In this scheme, the term “subnet” is used describe a cluster of network components that includes a server and several clients associated therewith (e.g., coupled through the wireless communication link). Depending on the context of the discussion however, a subnet may also refer to a network that includes a client and one or more subclients associated therewith. A “client” is a network node linked to the server through the wireless communication link. Examples of clients include audio/video equipment such as televisions, stereo components, personal computers, satellite television receivers, cable television distribution nodes, and other household appliances.
Server
12
may be a separate computer that controls the communication link, however, in other cases server
12
may be embodied as an add-on card or other component attached to a host computer (e.g., a personal computer)
13
. Server
12
has an associated radio
14
, which is used to couple server
12
wirelessly to the other nodes of subnet
10
. The wireless link generally supports both high and low bandwidth data channels and a command channel. Here a channel is defined as the combination of a transmission frequency (more properly a transmission frequency band) and a pseudo-random (PN) code used in a spread spectrum communication scheme. In general, a number of available frequencies and PN codes may provide a number of available channels within subnet
10
. As is described in the co-pending application cited above, servers and clients are capable of searching through the available channels to find a desirable channel over which to communicate with one another.
Also included in subnet
10
are a number of clients
16
, some of which have shadow clients
18
associated therewith. A shadow client
18
is defined as a client which receives the same data input as its associated client
16
(either from server
12
or another client
16
), but which exchanges commands with server
12
independently of its associated client
16
. Each client
16
has an associated radio
14
, which is used to communicate with server
12
, and some clients
16
may have associated subclients
20
. Subclients
20
may include keyboards, joysticks, remote control devices, multi-dimensional input devices, cursor control devices, display units and/or other input and/or output devices associated with a particular client
16
. A client
16
and its associated subclients
20
may communicate with one another via communication links
21
, which may be wireless (e.g., infra-red, ultrasonic, spread spectrum, etc.) communication links.
Each subnet
10
is arranged in a hierarchical fashion with various levels of the hierarchy corresponding to levels at which intra-network component communication occurs. At a highest level of the hierarchy exists the server
12
(and/or its associated host
13
), which communicates with various clients
16
via the wireless radio channel. At other, lower levels of the hierarchy the clients
16
communicate with their various subclients
20
using, for example, wired communication links or wireless communication links such as infrared links.
Where half-duplex radio communication is used on the wireless link between server
12
and clients
16
, a communication protocol based on a slotted link structure with dynamic slot assignment is employed. Such a structure supports point-to-point connections within subnet
10
and slot sizes may be re-negotiated within a session. Thus a data link layer that supports the wireless communication can accommodate data packet handling, time management for packet transmission and slot synchronization, error correction coding (ECC), channel parameter measurement and channel switching. A higher level transport layer provides all necessary connection related services, policing for bandwidth utilization, low bandwidth data handling, data broadcast and, optionally, data encryption. The transport layer also allocates bandwidth to each client
16
, continuously polices any under or over utilization of that bandwidth, and also accommodates any bandwidth renegotiations, as may be required whenever a new client
16
comes on-line or when one of the clients
16
(or an associated subclient
20
) requires greater bandwidth.
The slotted link structure of the wireless communication protocol for the transmission of real time, multimedia data (e.g., as frames) within a subnet
10
is shown in FIG.
2
. At the highest level within a channel, forward (F) and backward or reverse (B) slots of fixed (but negotiable) time duration are provided within each frame transmission period. During forward time slots F, server
12
may transmit video and/or audio data and/or commands to clients
16
, which are placed in a listening mode. During reverse time slots B, server
12
listens to transmissions from the clients
16
. Such transmissions may include audio, video or other data and/or commands from a client
16
or an associated subclient
20
. At the second level of the hierarchy, each transmission slot (forward or reverse) is made up of one or more radio data frames
40
of variable length. Finally, at the lowest level of the hierarchy, each radio data frame
40
is comprised of server/client data packets
42
, which may be of variable length.
Each radio data frame
40
is made up of one server/client data packet
42
and its associated error correction coding (ECC) bits. The ECC bits may be used to simplify the detection of the beginning and ending of data packets at the receive side. Variable length framing is preferred over constant length framing in order to allow smaller frame lengths during severe channel conditions and vice-versa. This adds to channel robustness and bandwidth savings. Although variable length frames may be used, however, the ECC block lengths are preferably fixed. Hence, whenever the data packet length is less than the ECC block length, the ECC block may be truncated (e.g., using conventional virtual zero techniques). Similar procedures may be adopted for the last block of ECC bits when the data packet is larger.
As shown in the illustration, each radio data frame
40
includes a preamble
44
, which is used to synchronize pseudo-random (PN) generators of the transmitter and the receiver. Link ID
46
is a field of fixed length (e.g., 16 bits long for one embodiment), and is unique to the link, thus identifying a particular subnet
10
. Data from the server
12
/client
16
is of variable length as indicated by a length field
48
. Cyclic redundancy check (CRC) bits
50
may be used for error detection/correction in the conventional fashion.
For the illustrated embodiment then, each frame
52
is divided into a forward slot F, a backward slot B, a quiet slot Q and a number of radio turn around slots T. Slot F is meant for server
12
-to-clients
16
communication. Slot B is time shared among a number of mini-slots B
1
, B
2
, etc., which are assigned by server
12
to the individual clients
16
for their

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