Pulse or digital communications – Systems using alternating or pulsating current – Plural channels for transmission of a single pulse train
Reexamination Certificate
1997-02-13
2001-09-18
Chin, Stephen (Department: 2634)
Pulse or digital communications
Systems using alternating or pulsating current
Plural channels for transmission of a single pulse train
C375S260000, C375S347000, C455S039000, C455S277200
Reexamination Certificate
active
06292516
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to a method and apparatus for communicating digital information packets, and more particularly to a method and apparatus for communicating packets with reduced errors while providing increased data throughput.
BACKGROUND OF THE INVENTION
In any wireless communication network there is a continued effort to achieve higher data exchange rates. Typically, digital data is exchanged wirelessly in the form of packets between two devices communicating with each other. Such packets are also commonly referred to as frames and represent a sequence of bits making up the digital information.
Referring briefly to
FIG. 1
, a packet
20
typically includes a preamble
22
, a data field
24
and an error detecting field
26
. The preamble
22
includes a synchronization pattern (not shown) which allows a device receiving the packet
20
effectively to lock-on to the packet
20
. The preamble
22
also typically includes a number of other control fields (not shown) which include such information as the source address, destination address, etc., of the packet
20
. The data field
24
includes the particular digital information intended to be communicated, sometimes referred to as the “payload”. The error detecting field
26
is normally located at the end of the packet as a means for checking the accuracy of a given transmission. For example, a cyclical redundancy code (CRC) value is commonly included in the error detecting field
26
.
A maximum length of a packet is determined primarily based on system tolerances for acceptable data bit error rate (BER) or frame error rate (FER) for transmissions between two devices. The longer in length the packet or frame, the more likelihood there will be an error which would require the packet to be re-transmitted.
A receiving device attempting to receive a frame or packet must determine whether the current signal-to-noise ration (S/N ratio) associated with a particular receiving antenna is sufficiently strong to receive the packet being transmitted. In receivers having two or more antennas which allow for antenna diversity, the S/N ratio associated with different antennas may differ thereby allowing the packet to be received by one antenna and not the other. The selection of which of several antennas to use while receiving a packet is conventionally done once at the start of reception of a packet. The selected antenna is then used to receive the remainder of the packet regardless of whether conditions change in the system which would otherwise have made one of the other antennas a better candidate for receiving at least a portion of the remainder of the packet.
In order to avoid having frame errors which would require the re-transmission of an entire packet, data in packets are often divided into several smaller packets having shorter lengths. For example,
FIG. 2
illustrates the manner in which the data field
24
of the packet
20
in
FIG. 1
can be divided into n (e.g., n=3) smaller packets. Each smaller packet includes a corresponding portion (e.g.,
24
a
-
24
c
) of the original data field
24
. The smaller length packets are then transmitted separately together with a corresponding preamble
22
and its own error detecting field
26
as represented in FIG.
2
.
By having smaller packet lengths, overhead associated with re-transmitting a single, long length packet may be reduced. Overhead associated with re-transmitting a packet may, for example, include the time it takes the receiving device to transmit a negative-acknowledgment indicating improper reception, time in generating another identical packet for transmission, and any additional time associated with waiting for the air to clear before re-transmitting the packet. By initially dividing data up into several packets having shorter lengths, time associated with transmitting and receiving the negative-acknowledgment can at least be avoided.
Unfortunately, even with dividing data up into several smaller packets, much of the overhead discussed can still exist. For instance, in order to send two consecutive packets which are relatively short in length the transmitting device must wait for an acknowledgment associated with transmission of a first packet before attempting to transmit a second packet. Additionally, even after receiving the acknowledgment, the transmitting device must still wait for the air to clear before transmission can begin for the second packet. Further, for each additional packet that is transmitted, there is extra overhead associated with including the preamble field and the detecting field.
In view of the aforementioned shortcomings associated with conventional data transmission, there is a strong need in the art for an improved method and apparatus which allows for reduced overhead associated with transmitting data. In particular, there is a strong need in the art for an apparatus and method which does not sacrifice data throughput.
SUMMARY OF THE INVENTION
According to one particular aspect of the invention, a method is provided for communicating a packet of digital information including at least a preamble with a synchronization pattern and a data field. The method includes the steps of including at least a plurality of test words at different respective locations in the data field; transmitting the packet as a whole including the test words from a transmitting device to a receiving device; receiving the packet with the receiving device; evaluating each of the plurality of test words in the received packet based on a comparison with a predefined criteria; and analyzing data reception properties associated with receiving the packet based on the evaluating step.
According to another aspect of the invention, a system is provided for communicating a packet of digital information including at least a preamble with a synchronization pattern, and a data field. The system includes means for including at least a plurality of test words at different respective locations in the data field; means for transmitting the packet as a whole including the test words from a transmitting device to a receiving device; means for receiving the packet with the receiving device; means for evaluating each of the plurality of test words in the received packet based on a comparison with a predefined criteria; and means for analyzing data reception properties associated with receiving the packet based on the evaluation performed by the means for evaluating.
In accordance with yet another aspect of the invention, a system is provided for communicating a packet of digital information including at least a preamble with a synchronization pattern and a data field. The system includes a transmitting device for transmitting the packet via a radio frequency (RF) signal, the transmitting device including: means for dividing the packet into a plurality of fragments and including test words in between consecutive fragments; and a transmitter for transmitting the packet as a whole including the test words via the RF signal; and a receiving device for receiving the packet from the transmitting device, the receiving device including: a receiver for receiving the packet via the RF signal; a plurality of antennas; a switch for determining which of the plurality of antennas provides the RF signal to an input of the receiver; a control circuit operatively connected to the switch for causing each of the plurality of antennas to be used in receiving at least a corresponding portion of each test word; an evaluation circuit for evaluating reception quality of the receiver using each of the plurality of antennas based on receiving the corresponding portion of each test word; and a selection circuit, governed by the evaluation circuit, for selecting one of the plurality of antennas to provide the RF signal to the input of the receiver during a portion of the packet subsequent to each test word.
According to still another aspect of the invention, a method is provided for communicating a packet of information in a wireless communication system. The method include
Dollard Michael S.
Petsko David P.
Arter & Hadden LLP
Chin Stephen
Cisco Technology Inc.
Liu Shu Wang
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