GB2448121A - A data distribution system employing two or more transmitters for improved transfer rate - Google Patents

Abstract

The invention concerns a data distribution system 1 comprising a source of data 7 and two or more wireless transmitters 3 for sending data to those mobile units 8 that respond to a broadcast search signal. By employing two or more transmitters 3 respectively designated to different sets of mobile identification codes, the number of mobile units 8 that can be fed with information in an acceptable time-frame is increased. The identification code of each mobile unit 8 that responds to the search signal is recorded 5 and the data 7 is transmitted to it from the transmitter 3 associated with that code. In this way, each transmitter 3 is required to serve only a proportion of the mobile units 8 that have responded to the search signal thereby greatly enhancing the speed at which the data 7 can be distributed.

Description

A Data Distribution System with lmi,roved Data Transfer Rate This

invention relates to a data distribution station having a source of data for distribution to mobile transceiver units within a limited range, means for broadcasting a search signal to the mobile units, means for receiving and storing codes identifying mobiles that have acknowledged receipt of the search signal, and a transmitter for transmitting the data to those mobile units.

Known systems of the aforementioned type are often deployed in situations where the number of users is potentially veiy large, with the result that long delays may be experienced by people wishing to receive content from the station. Examples of such situations are information points at trade shows, music festivals, bus or train stations, or museums at which significant number of people may wish to receive content in a relatively short period of time. Conventionally, some such systems have used a short range (up to about 10 metres) radio communication system known by the trade mark Bluetooth of Bluetooth SIG, Inc. The bandwidth of Bluetooth data transmission to consumer mobile devices varies greatly, but can be as low as 20 Kbytes per second and more typically 150 Kbytes per second, with the result that most transfers of digital audio or image content take several seconds, even a minute, to complete. As a result, a data distribution station capable of several simultaneous transfers at the full data rate might at best only be able to service in the region of 10 to 20 mobile devices per minute. For large content files such as video, with correspondingly longer transfer times, this problem becomes much greater. For example, if the data to be transferred is a thirty second video, this might typically take 30 seconds to transfer at a download speed of 150 Kilobytes per second, depending on the mobile device. If there are say6 mobile devices connected, one of these would have to wait 2.5 minutes before a connection is made or all six devices would face a download lasting 3 minutes. Mobile users are unlikely to tolerate a wait of this length of time.

A simple response to this problem is to provide duplicate wireless servers in each location to cope with the volume of usage. However, if these servers are separate units, this may not be an effective solution, because there is no sharing of information about which consumer devices have been served, and which are still awaiting attention. The result of this can be data being sent repeatedly to some mobile devices, while others are ignored completely.

Multiple server units within a data distribution station could be networked so as to share information to avoid this problem, but this may not be feasible, since the server units are often low-cost embedded devices with limited networking capabilities.

There may be further problems in networking in some environments, such as outdoor venues or in other circumstances where it is impracticable to run cables between the server units.

According to the invention there is provided a data distribution station comprising a source of data for distribution to mobile transceiver units within a limited range of the distribution station, means for broadcasting a search signal from the distribution station to the mobile units, means for receiving and storing codes identifying mobiles that have acknowledged receipt of the search signal, and a transmitter for transmitting the data to those mobile units; characterised in that the data distribution system comprises two or more transmitters, means for associating the different transmitters with respective different subsets of possible mobile identification codes, and means for transmitting the data to a mobile unit using the transmitter that is thus associated with the subset of codes containing that mobile unit's identification code.

By employing the invention it becomes possible to employ multiple transmitters within a single station without the need for communication between them.

When reference is made in this specification to a "station" it is important to understand that this can take a number of very different forms. For example it could -3.

be a discrete physical unit having a casing containing its electronic components. The casing could be purpose made as a data source or could have a different primary purpose perhaps related to an article to which the data relates. For example a data station relating to a painting in an art gallery could be embedded in the frame of the painting. There are however other important situations where the data distribution station has no housing or enclosure and where the different transmitters or servers are grouped together to form a "station" only in the sense that they are sufficiently close so that each of them would, if the invention were not implemented, be able to try to establish conflicting connections to the same mobile unit.

Every Bluetooth device has a unique 48-bit address by which it can be identified, and this is the first piece of information that a transmitter set to act as a "master" discovers as it scans for devices in its area. In the simplest case, the system could have just two Bluetooth or similar wireless devices close together at a single data station configured so that one services only devices with an odd-numbered Bluetooth address, and the other services only those with an even address. In this way each deals with half the devices within range, and thus the capacity of the overall system is double that of a single server, without requiring the two to communicate.

It is preferred that each transmitter should have its own associated memory and that identical data be entered into the memories of all the transmitters. This eliminates the need for any interconnection between the transmitters. However, where limited connectivity between the transmitters is possible, there could be a common store for this data, accessible by each of the transmitters. A facility could be provided whereby each server is configured to periodically act as a slave whereby any data that it does not already have is automatically acquired from adjacent servers.

One embodiment of the invention will now be described by example with reference to the accompanying single drawing which illustrates very schematically, a data station constructed in accordance with the invention.

Referring to the drawing there is shown a data station I at a publicly available location which will be assumed for the purpose of this description to be a bus stop.

The data station includes a number N of short range wireless servers 2 which, in this particular embodiment have no data or signalling connection between them. These wireless servers are all identical so just one will be described.

Each server comprises a readily available Bluetooth chip, defining functional blocks 3, 4, 5 and 6. The block 3 is a short range radio transceiver operating within the bandwidth of 2.402 GHz and 2.480 GHz. The filter 4 is defined by suitable programming of the chip to define a set of mobile identity codes which the server is to serve.

Generally, a set of N servers, each associated with a distinct value of n, where 0 < n <= N-i, could be configured so that each one services only those consumer devices whose Bluetooth address BA has the property: BAinodN=n That is, the Bluetooth address divided by the number of servers gives a remainder equal to the number of the given server. In this arrangement it is necessary to configure each server with the total value N, i.e. the number of servers in the data station 1, and the individual value n, i.e. the unique value of this server. In the simple case of an isolated server, these values would be N = i, n = 0, allowing it to match any Bluetooth address.

In operation the transceiver 3 in each server 2 acts as a "master" and broadcasts a search signal at a frequency that hops in a random-like way between frequencies within a broad range of frequencies. The frequency hopping takes place at a frequency that is typically 1600Hz. Each mobile unit 8 has a tuneable receiver which, when switched to a discover' mode, is caused to hop between the same frequencies as the master, also in a random-like way but at a significantly slower switching rate than that of the master 3. The master 3 will at some point broadcast its search signal on the same frequency as that to which the mobile, which acts as a "slave" is currently tuned. Receipt of the broadcast by the mobile causes the latter to respond giving, inter alia, its identity code. This is checked at 4 to ascertain whether it belongs to the set of identity codes that have been assigned to the server. If it does belong to that set, then the code is stored at 5. The store 5 thus accumulates a list of the IDs of all the mobiles (a) which are in range and (b) for which the short range communication thcility is switched on and (c) which have an identity code assigned to the relevant server by the programming entered into the filter 4. The server then enters a connection mode during which it hops between channels, broadcasting the fact that it is looking for the mobiles identified by the stored IDs and inviting them to receive data. The user of any of these mobiles, wishing to receive the data may accept the invitation, whereupon a data communication channel called a "piconet" is established by the server. For this purpose, the server defines a pseudo-random frequency hopping sequence using the ID and clock of the server. This sequence is transmitted to the mobile and data can then be transferred between the two devices over the established frequency hopping connection. Data is transferred in packets between each frequency hop.

Any mobile wishing to acquire information from the data station can establish a connection for that purpose with an associated server 2 in the data station and, because each server is allowed to make connection with only a fraction of these mobile units, the transfer of data to them can take place relatively rapidly.

it is emphasised that the particular embodiment of the invention that has been described is just one example of how the invention, as defined by the following Claims, may be implemented. In alternative embodiments the manner in which different mobile IDs are assigned to the different servers could differ from that described using algorithms which result in a more random-like set of mobile IDs being associated with the different servers, the only requirement being that these sets of IDs should be mutually exclusive. The system, which we have described as "wireless" can operate in a frequency specirum of between 2.402 GHz and 2.480 GHz, as in Bluetooth, or in any other frequency of the electromagnetic spectrum including infrared and microwaves, or it could be based on acoustic or any other radiated signals. Although it is envisaged that the "data station" will often be at a fixed location, this is not necessary for the functioning of the invention and it could be located on a moving platform or vehicle or could be hand held. Furthermore, the data store, indicated at 5 on the figure, instead of being duplicated in each wireless server, could be replaced by a single store linked to each server in the data station.

Claims (6)

1. Claims 1 A data distribution station comprising a source of data for

   distribution to mobile transceiver units within a limited range of the distribution station, means for broadcasting a search signal from the distribution station to the mobile units, means fbr receiving and storing codes identifying mobiles that have acknowledged receipt of the search signal, and a transmitter fbr transmitting the data to those mobile units; characterised in that the data distribution station comprises two or more transmitters, means for associating the different transmitters with respective different subsets of possible mobile identification codes, and means for transmitting the data to a mobile unit using the transmitter that is thus associated with the subset of codes containing that mobile unit's identification code.
2. 2. A data distribution station according to Claim 1 characterised in that: each transmitter has a store for storing mobile identification codes of mobiles that have indicated their user's desire to receive the data and that belong to the sub-set associated with that transmitter; and a controller for causing the transmitter to transmit the data to the mobile units whose identities are held in the store.

   3. A data distribution station according to Claim 1 or 2 characterised in that each transmitter has its own memory and in which the same data is held in each memory.
3. 3. A wireless data distribution station constructed in accordance with any preceding Claim having a range of no more than about 10 metre.
4. 4. A data distribution station according to any preceding Claim located at a place available to the public and in that the data is associated with that location.
5. 5. A data distribution station according to any preceding claim characterised in that each transmitter is a radio transmitter.
6. 6. A data distribution station according to Claim 5 characterised in that the transmitters operate in a spectrum between 2. 402 GHz and 2.480 GHz.