Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
2000-05-11
2004-07-06
Tu, Christine T. (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C714S712000, C714S821000
Reexamination Certificate
active
06760877
ABSTRACT:
The present invention relates to a method in a wireless communication system as set forth in the preamble of the appended claim
1
. The invention relates also to a wireless communication system as set forth in the preamble of the appended claim
15
.
A considerable increase in the use of information services as a result of an increase in particularly the Internet and so-called World Wide Web (WWW) services has brought about a need to develop faster communication services for transferring information between a provider of an information service and a terminal using the information service. Furthermore, several information services also comprise so-called multimedia information, such as images, video images, and sound. The transmission of such multimedia information requires a high data transmission rate to execute the data transmission as close to real time as possible.
Communication systems intended for an office environment, so-called local area networks (LAN), are to a great deal implemented as wired systems. Thus, the data transmission connection between terminals and a server is implemented either electrically via a cable or optically via an optical fibre. It is an advantage of such a fixed system that relatively high data transmission rates can be achieved. A drawback in such a fixed communication network is that it is difficult to make changes, and the terminals must usually be placed relatively close to connection points intended for them, whereby the movability of the terminal is affected. The implementation of such a wired local area network in an already existing building is not always successful, or the wiring of cables afterwards is expensive. On the other hand, a communication cable system which may already exist particularly in older buildings is not necessarily suitable for fast data transmission.
For implementing local area networks, there are several wireless communication systems under development. Several wired communication systems are based on the use of radio signals in data transmission.
One such communication system for a local area network based on radio communication is the so-called HIPERLAN (Hlgh PErformance Radio Local Area Network). Such a radio network is also called a broadband radio access network (BRAN).
In version
2
of the HIPERLAN communication system under development, the aim is to achieve a data transmission rate of even more than 30 Mbit/s, the maximum cell range being some tens of metres. Such a system is suitable for use in the same building e.g. as an internal local area network for one office. There is also a so-called HIPERACCESS communication system under development, in which an aim is to achieve the same data transmission rate as in said HIPERLAN/2 communication system but with the cell range of some hundreds of metres, wherein the HIPERACCESS system is applicable for use as a larger local area network e.g. in schools and larger building complexes.
In the HIPERLAN/2 system which is used as an example, the frame structure used in the data link layer DLC is shown in a reduced manner in the appended
FIG. 1
b
. The data frame FR consists of control fields C, such as RACH (Random Access CHannel), BCCH (Broadcast Control CHannel) and FCCH (Frame Control CHannel), as well as a data field D which comprises a given number of time slots TS
1
, TS
2
, . . . , TSsn, in which it is possible to transmit actual payload information.
Each control field C as well as the packets to be transmitted in the time slots of the data field preferably comprise error checking data which has been calculated by an access point AP
1
that transmits the data frame and added into the control fields C of the data frame and to the packets to be transmitted in the time slots TS
1
, TS
2
, . . . , TSn. This checking data is preferably a checksum calculated on the basis of information contained in said field, such as CRC (Cyclic Redundancy Check). In the receiving wireless terminal MT
1
, it is possible to use the error checking data to examine if the data transmission possibly contained any errors. There can also be several such error check data in the field C, D, calculated on part of the information contained in the field. For example in the HIPERLAN/2 system, the FCCH control field consists of smaller information elements, for which error checking data is calculated respectively. The number of these information elements may vary in each data frame. All data frames do not necessarily have an FCCH control field, in which case the number of information elements is zero.
Communication in the HIPERLAN/2 system is based on time division multiple access TDMA, wherein there can be several connections simultaneously on the same channel, but in said frame each connection is allotted a time slot of its own, in which data is transmitted. Because the quantity of data to be transmitted is usually not constant in all the simultaneous connections, but it varies in time, a so-called adapted TDMA method is used, in which the number of time slots to be allocated for each data transmission connection may vary from zero to a maximum, depending on the loading situation at each time as well as on the data transmission capacity allocated for the connection.
For the time division multiple access to work, the terminals coupled to the same node must be synchronized with each other and with the transmission of the node. This can be achieved for example in such a way that the receiver of the wireless terminal receives signals on a channel. If no signal is detected on the channel, the receiver shifts to receive on another channel, until all the channels are examined or a channel is found on which a signal is detected that is transmitted from an access point. By receiving and demodulating this signal, it is possible to find out the time of transmission of the control channel BCCH of the access point in question and to use this to synchronize the terminal. In some cases, the terminal may detect a signal from more than one access points, wherein the terminal preferably selects the access point with the greatest signal strength in the receiver and performs synchronization to this access point.
After the terminal is synchronized to the access point, the terminal can start a connection set-up to couple to this access point. This can be performed preferably so that the terminal transmits a connection set-up request to the access point on the RACH control channel. In practice, this means that the terminal transmits in a time slot allocated for the RACH control channel and the access point simultaneously listens to communication on the channel, i.e. receives signals on the channel frequency used by the same. After detecting that a terminal is transmitting a connection set-up request message, the access point takes the measures required for setting up the connection, such as resource allocation for the connection, if possible. In the resource allocation, the quality of service requested for the connection is taken into account, affecting e.g. on the number of time slots to be allocated for the connection. The access point informs the terminal if the connection set-up is possible or not. If it has been possible to set up a connection, the access point transmits in the BCCH control field information e.g. on the transmission time slots, receiving time slots, connection identifier, etc. allocated for the connection. The number of transmission and receiving time slots is not necessarily the same, because in many cases the quantity of information to be transmitted is not the same in both directions. For example, when an Internet browser is used, considerably less information is transmitted from the terminal than information is received to the terminal. Thus, for the terminal, fewer transmission time slots are needed than receiving time slots. Furthermore, the number of time slots allocated for the connection may preferably vary in different frames according to the need to transmit information at the time. The access point controller is provided with a so-called scheduler, which serves e.g. the purpose o
Lappeteläinen Antti
Smolander Visa Tapio
Nokia Mobile Phones Ltd.
Perman & Green LLP
Tu Christine T.
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