Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1999-12-28
2003-11-04
Ton, Dang (Department: 2666)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S344000
Reexamination Certificate
active
06643278
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
BACKGROUND OF THE INVENTION
The present embodiments relate to wireless communication systems, and are more particularly directed to such systems using frequency hopping.
Wireless networks are becoming increasingly popular, and in this regard there has been improvement in many aspects of such networks. Some improvements relate to configurations that permit simultaneously operation of different networks where there is minimal or no interference between communications belonging to each of the networks. In this respect, the term network is used, and is further used in the same manner for the remainder of this document, to describe a system consisting of an organized group of intercommunicating devices. Further in this respect, the different networks may be labeled according to a first network that is already transmitting in time followed by a second network in time seeking to transmit and thereby possibly communicating and causing interference due to a communication overlapping the pre-existing communication of the first network. Accordingly, to facilitate the remaining discussion, such a first network is referred to as an incumbent network, while the network which seeks to communicate, or in fact does communicate, after the incumbent network is referred to as the newly-entering network. Given this terminology, the present background and embodiments discussed below are directed to reducing interference between incumbent network communications and newly-entering network communications.
One approach to reducing the above-introduced interference is known in the art as spread spectrum frequency hopping and is sometimes referred to more simply as frequency hopping. In frequency hopping, a newly-entering network transmitter transmits packets of information at different frequencies in an effort to reduce the chance that the packet will interfere or “collide” with a packet transmitted at a frequency by a transmitter in an incumbent network. The change between frequencies, that is, from one frequency to another, is said to be a “hop” between the frequencies. Moreover, the goal is such that each packet from a newly-entering network is transmitted at a frequency which neither overlaps nor is near enough to a frequency at which an incumbent network is transmitting. Further in this regard, some systems (e.g., using Bluetooth protocol) transmit each successive packet at a different frequency, that is, the transmitter is “hopping” to a different frequency for each packet. Alternatively, others systems (e.g., IEEE 802.11) transmit a first set of packets at a first frequency, and then hop to a second frequency to transmit a second set of packets, and so forth for numerous different sets of packets at numerous different respective frequencies. Note further that if interference or a collision does occur, it typically corrupts the data of both packets, that is, the data transmitted by both the newly-entering network and the incumbent network. As a result, both networks are then required to re-transmit the packets an additional time so as to replace the corrupted data resulting from the collision.
In an effort to achieve minimal packet collision using frequency hopping, two prior art methods have arisen for determining the different frequencies to which a network will hop. In a first method, a frequency hopping network uses a pre-ordained hopping sequence. This first approach is used by way of example under the IEEE 802.11 standard. In a second method, a seed is provided to a pseudo-random generator which produces a corresponding pseudo-random series of frequencies along which the network hops. This second approach is used by way of example under the fairly recently developed Bluetooth protocol. Both of these approaches have achieved some level of success in reducing the amount of inter-network packet collision. Nevertheless, the present inventors have empirically determined that by locating two or more different networks in the same vicinity such that transmissions from each different network effectively compete for airtime, there still arises a considerable amount of packet collisions, thereby reducing the effective transmission rate for each network.
Frequency hopping as described thus far reduces the chances of interference between a packet from newly-entering network and a packet from an incumbent network. Further in this regard and by way of additional background,
FIG. 1
illustrates communications of such packets and, as detailed below, it also illustrates instances where packet collisions occur. Looking to
FIG. 1
in greater detail, its horizontal axis illustrates time (or time slots), and its vertical axis indicates frequency. Additionally,
FIG. 1
illustrates a number of blocks, where each block is intended to depict a packet as transmitted by either an incumbent network or a newly-entering network. Further in this regard, note that the term “packet” is used in this document to define a block of information sent in a finite period of time, where subsequent such packets are sent at other times. This block of information may take on various forms, and sometimes includes different information types such as a preamble or other type of control information, followed by user information which is sometimes also referred to as user data. Further, the overall packet also may be referred to in the art by other names, such as a frame, and thus these other information blocks are also intended as included within the term “packet” for purposes of defining the present inventive scope. In any event, returning to
FIG. 1
, for the sake of reference, each packet illustrated in
FIG. 1
is labeled with an identifier using the letter “P” (i.e., for packet) and following after that letter is a number corresponding to the network which transmitted the packet. More particularly, packets transmitted by the first network (i.e., the incumbent network) are labeled with an identifier P
1
while packets transmitted by the second network (i.e., the newly-entering network) are labeled with an identifier P
2
. Further, the subscript for each packet identifies a time period encompassed by the duration of the packet. For example, during a time to, the first network transmits a packet P
1
0
while also during time t
0
the second network transmits a packet P
2
0
. Further in this regard, in the prior art transmissions by the first network are asynchronous with respect to transmissions of the second network, both in start time and periodicity. Thus, time t
0
is only meant as a relative indication for the first packet from each network, and it is not intended to suggest that the packets from both networks begin and end at the same time.
With respect to all packets in
FIG. 1
, the preceding demonstrates that each packet begins at a certain time, ends at a later time, and fills a certain frequency range (where the range is referred to as a channel). As a result and as described below, interference may occur if the area in
FIG. 1
defined by a packet overlaps or is within a certain distance of a packet from another wireless link. Indeed and as discussed below, such interference may occur in one of four different ways.
Time t
1
in
FIG. 1
illustrates a first type of packet interference, where it may be seen that the first network transmits a packet P
1
1
After packet P
1
1
commences but also during time t
1
the second network transmits a packet P
2
1
. The overlap of packets P
1
1
and P
2
1
is shown as a first collision C
1
. Note that the horizontal alignment of packets P
1
1
and P
2
1
graphically indicates that in the example of collision C
1
, both packets occupy the same frequency channel. Thus, collision C
1
represents an example where two different networks attempt to transmit packets during an overlapping time period and along the same channel.
Before proceeding with other types of packet collisions, an additional discussion is noteworthy with respect to a methodology which
Panasik Carl M.
Siep Thomas M.
Brady III Wade James
Neerings Ronald O.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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