Periodic wireless broadcast

Details Periodic wireless broadcast Periodic wireless broadcast

1998-11-05

2003-02-25

Ton, Dang (Department: 2661)

Multiplex communications

Communication over free space

Combining or distributing information via time channels

C370S480000

Reexamination Certificate

active

06526038

ABSTRACT:

FIELD OF THE INVENTION
The present invention is directed to an improved periodic wireless data broadcast and, more particularly, to (1) an improved method of arranging data on a periodic broadcast and (2) an improved signal structure for such broadcasts.
BACKGROUND OF THE INVENTION
Delivering information via wireless transmission is becoming increasingly popular. As seen in
FIG. 1
, information, such as stock prices, traffic information, weather reports, airline schedules, and sports scores, may be broadcast from a single source, such as a service provider
30
(not unlike a cellular phone service provider) to a number of recipients (users)
32
via a wireless transmission media. These media may be, for example, paging networks, FM subcarrier networks, cellular phone networks, and PCS (personal communications services) networks. This application will refer to the media simply as a “wireless media network”.
A user
32
may be a person having a wireless terminal
34
, such as a personal digital assistant (PDA), as is illustrated in FIG.
1
. (The wireless terminal
34
is often referred to as a “client”, and the ultimate human recipient of the information is referred to as a “user”.) A PDA is typically a laptop or palmtop computer connected to a wireless media network. The wireless terminal
34
usually is not connected to any direct power source, but rather runs on either conventional or rechargeable batteries. Because wireless terminals are often used away from the home or office, it is an important consideration of a wireless terminal user to maximize the length of time that the terminal may operate without having to change or recharge batteries. Thus, it is important to minimize the power consumption necessary for the client to receive, decode, and display information received over the wireless data network, thus increasing the useful life of the battery.
One method of transmitting information over a wireless network is to broadcast the information periodically. This method is well-known and has been discussed in Imielinski et al, “Energy Efficient Indexing on Air”, Proc. ACM SIGMOD Conference, May, 1994. In August 1994 we noted the similarity of this method to the method of writing data on a standard rotating magnetic disk, and thus called the method an “airdisk” by analogy. Subsequently, Zdonik et al, “Are ‘Disks in the Air’ Just Pie in the Sky?”, Proc. IEEE Workshop on Mobile Computing Systems and Applications, Dec. 8-9, 1994, also noted this similarity, and called this method a “broadcast disk”. An “airdisk” is a periodic transmission of data over a wireless network. It is called an airdisk because it may be theoretically compared to a rotating data disk, as will be illustrated below.
FIG. 2
shows a periodic broadcast
40
having a number of transmissions (the arrow indicates increasing time). A first transmission
50
includes the following sequence of topics: stock prices
51
, traffic
52
, weather
53
, airline schedules
54
, and sports scores
55
. After the transmission
50
is complete, a new transmission
60
is immediately sent, beginning with, in this example, stock information
61
, traffic
62
, etc. Each transmission may begin with a preamble
56
,
66
indicating the beginning of a transmission. The preamble may be followed by an index
57
,
67
which indicates the location of the beginning of each topic in the transmission. Each topic
51
-
55
,
61
-
65
may begin with a topic header
58
,
68
which indicates the start of a topic. Each transmission may end with a trailer
59
,
69
indicating the end of a transmission.
Although the example in
FIG. 2
shows the broadcast is composed of different items defined as topics of information (stock prices
51
, traffic
52
, etc.), it could just as well be the case that the broadcast contains items which relate to a single topic. For example,
FIG. 2
could refer to stock prices only, with a first transmission including the following sequence of items which relate to a single topic: IBM price, NYNEX price, HP price, and so on. This discussion often refers to “topics” for illustration. In most instances, however, the illustration is equally applicable to smaller items, such as information about particular stocks, traffic conditions on certain roadways, or weather conditions for a certain geographic region.
The broadcast
40
is periodic because each transmission is immediately followed by another. As seen in
FIG. 3
, the periodic broadcast
40
of
FIG. 2
may be theoretically compared to a revolving disk
70
(i.e., such as a computer or optical disk) and a read head
80
(i.e., such as a magnetic or optical head) (the arrow indicates the direction of disk rotation). The disk in this illustration is separated into five radial portions called sectors. These sectors contain stock
71
, traffic
72
, weather
73
, airline
74
, and sports
75
information, respectively. Protocol related portions of the signal such as the preamble, the index, the headers, and the trailer are omitted for simplicity. After a complete rotation of the disk
70
, the same sector is presented to the head
80
for reading. Similar to a computer disk, the periodic broadcast
40
may be updated by the service provider
30
so that subsequent rotations may include revised, additional, or altered data; and the data may be presented in a different sequence.
Much of the information on the airdisk is dynamic—for example, stock prices, sports scores, weather, and traffic conditions may change throughout the day. Thus, after a period of time some information transmitted in a periodic broadcast may become “stale” and is of little use to the user
32
(i.e., hours old stock prices during active trading). Thus, the amount of time it takes a client
34
to access all of the desired information (referred to as “access latency”) is one measure of performance for an airdisk transmission. Also, because many periodic broadcast clients may be wireless terminals, where power efficiency is a major concern, power a consumption may be minimized by the ordering of the data in the transmission. This is illustrated in
FIGS. 4
a
and
4
b.
Using the rotating disk analogy,
FIGS. 4
a
and
4
b
show the importance of data ordering in instances where the transmission is not indexed and indexed, respectively. Using an index in a periodic transmission is discussed in the Imielinski et al. paper cited above.
Where the transmission has no index, the receiver, such as a wireless terminal
34
, must be on at all times to determine whether it is receiving information it is interested in so that it may read this information. This constant monitoring of the incoming transmission inefficiently consumes power. Alternatively, if all of the information sections are of equal size—and thus of equal time length—the terminal
34
could be programmed to turn on at the beginning of each section and quickly determine if the section includes data desired to be read. This alternative conserves power but may be impractical because the sections may be of differing lengths and because the information is dynamic, each section may be a different length each broadcast. (Unlike a physical disk, an airdisk may increase or decrease in size if information is added or deleted to a topic.) If the sections are certain types of data items, such as stock prices, however, the items may be arranged to have identical lengths.
An index may be provided at the beginning of each transmission giving the sequence of topics and the location of the beginning of each topic in the upcoming transmission. This is advantageous because it allows the terminal
34
to be “off” (i.e., consuming a reduced amount of power) except when desired information is being broadcast. This reduces the “on” time for the wireless transmitter
34
and conserves power. An index may be disadvantageous, however, because it requires additional data to be included in the broadcast. This makes the airdisk “larger” and takes a longer time to transmit the entire periodic broadcast.
FIG. 4
a
illustrates the access latency for an uni

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