Telecommunications – Transmitter and receiver at separate stations – Having measuring – testing – or monitoring of system or part
Reexamination Certificate
2000-11-16
2003-12-30
Nguyen, Lee (Department: 2682)
Telecommunications
Transmitter and receiver at separate stations
Having measuring, testing, or monitoring of system or part
C455S562100, C370S245000
Reexamination Certificate
active
06671495
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method in a wireless communication system according to the preamble of the appended claim 1. The invention also relates to a wireless communication system according to the preamble of the appended claim 11. The invention also relates to a wireless terminal according to the preamble of the appended claim 21 and to an access point according to the preamble of the appended claim 22.
2. Brief Description of Related Developments
Communication systems intended for an office environment, so-called local area networks (LAN), are primarily implemented as wired systems. Thus, the connection between the terminals and the server is implemented either electrically by means of a cable or optically by means of an optical fibre. An advantage of such a fixed system is, for example, the possibility to achieve relatively high data transmission rates. A disadvantage of such a fixed communication system is that it is difficult to make changes, and the terminals must usually be placed relatively close to connection points intended for them, which affects the movability of the terminal. The implementation of such a wired local area network in an already existing building is not always possible, or it is expensive to install the cables afterwards. On the other hand, particularly in older buildings, there possibly already exists a communication cabling which is not necessarily suitable for fast data transmission.
There are various wireless communication systems under development for implementing local area networks. Several wireless communication systems are based on the use of radio signals in data transmission. One such communication system for a local area network under development, based on radio communication, is the so-called HIPERLAN (High 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 connection distance 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 the aim is to achieve the same data transmission rate as in said HIPERLAN/2 communication system, but the aim is to achieve a connection distance of several hundreds of metres, wherein the HIPERACCESS system is suitable for use as a regional local area network for example in schools and larger building complexes.
In the data link layer DLC of the HIPERLAN/2 system used as an example, the MAC (Medium Access Control) frame structure is illustrated 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 of a data field D which comprises a certain number of time slots TS
1
, TS
2
, . . . , Tsn, 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 contain error check data which is calculated by the access point AP
1
transmitting the data frame and added into the control fields C of the data frame and the packets to be transmitted in the time slots TS
1
, TS
2
, . . . , TSn. This check 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 check data to examine whether there were possible errors in the data transmission. The field C, D may also contain several items of such check data calculated from part of the information contained in the field. For example in the HIPERLAN/2 system, the FCCH control field consists of smaller information elements, check data being calculated for each of them. The number of these information elements can vary in each data frame. All data frames do not necessarily have an FCCH control field, wherein also the number of information elements is zero.
Data transmission in the HIPERLAN/2 system is based on time division multiple access TDMA, wherein there can be several simultaneous connections on the same channel, but each connection is allocated a separate time slot in said frame, wherein data is transmitted. Because the quantity of data to be transmitted is normally not constant in all the simultaneous connections, but it varies with time, a so-called adapting TDMA method is used, wherein 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 each time as well as on the data transmission capacity allocated for the connection.
For 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 a signal is not detected on the channel, the receiver changes over to receive on another channel, until all the channels have been examined or a channel is found on which a signal transmitted by an access point is detected. By receiving and demodulating this signal, it is possible to determine the moment of transmission of the control channel BCCH of the access point in question and to synchronize the terminal on the basis thereof. In some cases, the terminal can detect the signal of more than one access point, wherein the terminal advantageously selects the access point which has the strongest signal in the receiver, and performs the synchronization with this access point.
When the terminal is synchronized with the access point, the terminal can initiate a connection set-up to couple to this access point. This can be conducted advantageously in such a way that the terminal transmits on the RACH control channel a connection set-up request to the access point. In practice, this means that the terminal transmits in the time slot allocated to the RACH control channel and at the same time the access point listens to the communication on the channel i.e. receives signals on the channel frequency it is using. When the access point detects that a terminal is transmitting a connection set-up request message, it performs the procedures necessary for the connection set-up, such as resource allocation for the connection, if it is possible. In the resource allocation, the quality of service requested for the connection is taken into account, which affects e.g. the number of time slots to be allocated for the connection. The access point informs the terminal whether the connection set-up is possible or not. If the connection set-up is successful, the access point transmits in the BCCH control field e.g. data on the transmission time slots, reception time slots, connection identifier, etc. which are allocated for the connection. The number of transmission and reception time slots is not necessarily the same, because in several cases the quantity of information to be transmitted is not the same in both directions. For example when using an Internet browser, the quantity of information transmitted from the terminal is considerably smaller than the amount of information received in the terminal. Thus, with respect to the terminal, the required number of transmission time slots is smaller than that of reception time slots. Furthermore, the number of time slots allocated for the connection can advantageously vary in different frames according to the need to transmit data. The access point controller is provided with a so-called scheduler, one function of which is the aforementioned allocation of time slots for different connections. The scheduler is implemented advantageously as an application program in the access point controller.
Since duplex da
Lappeteläinen Antti
Salokannel Juha
Smolander Visa
Nguyen Lee
Nokia Corporation
Perman & Green LLP
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