CN1244979A - SDMA packet radio system and channel establishment method - Google Patents

Abstract

The invention relates to a packet radio system and a method using SDMA for channel establishment. The packet radio system comprises a network part (100), at least one subscriber terminal (102) and a duplex radio connection (104) between the network part (100) and a subscriber terminal (102). The duplex radio connection (104) is used for connection set-up and packet transmission. The invention is characterized in that for connection set-up the network part (100) and the subscriber terminal (102) are arranged to establish a special channel (210) with a significantly longer range than that of a normal channel (200). The special channel (210) has a bit energy-to-noise ratio of about 5-12 dB better than the normal channel (200).

Description

SDMA Packet Wireless System and Channel Estimation Method

The invention relates to a packet radio system using SDMA, said system comprising a network part, at least one user terminal, and a two-way radio connection between the network part and the user terminal for connection establishment and packet transmission.

A packet radio system refers to a radio system using packet switching techniques well known in fixed networks. It corresponds to circuit-switched wireless systems. Circuit switching is a method of establishing connections between users that allocates a predetermined amount of transmission capacity to the connection. The transmission capacity is dedicated to the wireless connection for the entire duration of the connection. Therefore, known wireless systems, such as the GSM 900/DCS 1800/PCS 1900 systems based on GSM, and the US wireless system using CDMA technology are circuit switched. A method of packet switching in which connections between users are established by sending data in packets containing address and control data. Multiple connections can use the same transport connection at the same time. In recent years, the use of packet-switched wireless systems, especially in data transmission, has been the subject of research, since packet switching is well suited, for example, to the transmission of data required by computer programs which generate in bursts the required sent data. In this case, the data transfer connection does not need to be occupied all the time, but only during packet transfer. This saves a lot of cost and capacity when constructing and using the network.

Research on packet wireless networks began in 1968 with the University of Hawaii's ALOHA project, in which a host computer was connected to a remote terminal via a wireless link. Packet radio networks are currently a very attractive object of further development of the GSM system, in which connection it is known as the General Packet Radio Service (GPRS). For example, the ETSI GSM specification (ETSI GSM03.64) describes the air interface between the network part and user terminals in GPRS.

In the GSM system, a physical channel is a time slot of a TDMA frame. A logical channel is either an ordinary channel or a dedicated channel. A TDMA frame includes 8 time slots. For dedicated channels, 26 multiframes 26 TDMA frames long are defined, using time slots 1-7 of the TDMA frame. The common channel defines 51 multiframes with a length of 51 TDMA frames correspondingly, using time slot 0 of the TDMA frame. Common channels include Broadcast Channel (BCH) and Common Control Channel (CCCH). BCH channels include Frequency Correction Channel (FCCH), Synchronization Channel (SCH) and Broadcast Control Channel (BCCH). CCCH channels include Paging Channel (PCH), Access Grant Channel (AGCH) and Random Access Channel (RACH). Dedicated channels include traffic channels (TCH) and dedicated control channels (DCH). DCH channels include Standalone Dedicated Control Channel (SDCCH), Slow Associated Control Channel (SACCH), and Fast Associated Control Channel (FACCH).

According to the aforementioned ETSI GSM specification 03.64, a physical channel, the Packet Data Channel (PDCH), is defined in packet radio systems for connection establishment and packet transmission, said channel being actually a traffic channel. In the PDCH channel, logical channels are further divided. Logical channels are divided into Packet Common Control Channel (PCCCH) and Packet Traffic Channels. Packet Traffic Channels include Packet Data Traffic Channel (PDTCH) and Packet Associated Control Channel (PACCH). The PCCCH channels include Packet Random Access Channel (PRACH), Packet Paging Channel (PPCH), Packet Grant Channel (PAGCH) and Packet Broadcast Control Channel (PBCCH).

In the description of this application, paging channels refer to those channels required by the packet radio system in operations associated with connection establishment and withdrawal, such as calling a user terminal, reserving a channel, and the like. For example in a conventional GSM system these channels are the PCH and AGCH channels in the downlink and the RACH channel in the uplink. In a GSM system using a packet radio system, the corresponding channels are the PPCH and PAGCH channels in the downlink and the PRACH in the uplink.

SDMA (Space Division Multiple Access) technology is used to increase the coverage area of dedicated channels in wireless systems. This is achieved using a smart antenna approach, whereby directional antenna beams are assigned to individual user connections. The orientation of the antenna beam is achieved either by physically moving the antenna to be oriented, or by electronically changing the radiation pattern of the antenna. The biggest problem is that when the connection is established, the position of the user terminal is unknown, so it is not possible to direct the antenna beam. In common wireless systems, one way to solve this problem is to increase the transmission power of the common channel required for connection establishment. This solution raises new problems because it is expensive and technically complex to implement. In addition, because GSM uses common traffic channels to transmit common channels, this solution is not suitable for GSM systems using GPRS. Another known solution is even less ideal: trusting that the common channel will work well below predetermined sensitivity values. This greatly impairs the operation of the system and the reliability of its operation. In packet radio systems, no system has been developed that works well.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a packet radio system which can efficiently use SDMA while avoiding the aforementioned problems.

This is achieved by the system described in the preamble, characterized in that, during connection establishment, the network part establishes a special channel whose scope is much larger than the normal channel.

The present invention also relates to a system described in the preamble, which is characterized in that, during the connection establishment process, the user terminal establishes a special channel whose range is much larger than that of an ordinary channel.

The invention also relates to a method for establishing a channel in a packet radio system using SDMA, said packet radio system comprising a network part, at least one user terminal, and a two-way radio connection between the network part and the user terminal, the two-way radio Connections are used for connection establishment and packet transfer.

The method is characterized in that the method includes the following steps: A) During the connection establishment process, a special channel is established, and its range is much larger than that of the common channel.

The system of the present invention has several outstanding advantages. Because SDMA technology can be used, the method of using directional antennas to increase cell coverage sets can be completely adopted. The payload bit energy-to-noise ratio of the sent call channel is greatly improved. This is because, for example in the case of narrowband special channels, the payload bit energy-to-noise ratio is inversely proportional to the transmitted bit rate when the transmission power is kept constant. This greatly increases the coverage area of the base station. For both the network part and the user terminal, this solution is technically easy to implement, and because no new components are required, the cost of equipment production will not be increased.

The method of the present invention provides the same advantages as the system described above. Obviously, different combinations can be produced by combining the preferred embodiment and the detailed embodiment to achieve the desired technical efficiency.

Describe the present invention in detail below in conjunction with the example shown in the accompanying drawing, in the accompanying drawing

Figure 1 illustrates a packet radio system;

Figure 2 illustrates an example of a normal carrier and a carrier containing special channels;

Figure 3 illustrates an example of a normal channel for an uplink connection;

Figure 4 illustrates an example of a special channel for an uplink connection;

Figure 5 illustrates the implementation of the system.

Let us examine Figure 1. The wireless system comprises a network part 100 and user terminals 102 with an intermediate two-way wireless connection 104 . The wireless connection 104 is used to transmit a wireless signal with a frame structure on a predetermined carrier frequency. In the GSM system, a frame consists of a number of time slots. In each time slot there is either a common channel or a dedicated channel.

According to the invention, the network part 100 and the user terminal 102 establish a special channel during connection establishment. The range of special channels is much larger than ordinary channels. The bit energy-to-noise ratio of this channel is 5-12 dB better than that of ordinary channels. Let us now examine Figure 2, which illustrates an example of a partial frequency range in a downlink connection of a GSM system. The distance between the midpoints of the carrier frequencies is 200kHz. The X-axis shows three channels 935.2MHz, 935.4MHz and 935.6MHz respectively. The Y axis shows the transmitted power. Waveforms 200, 202 illustrate common channels for packet transmission. Waveform 210 illustrates how a 200 kHz frequency band typically comprising one channel narrows down to a width of 25 kHz. Thus, it narrows at a ratio of 1:8. The ratio of narrowing can vary from 1:3 to 1:16. Because the capacity of the channel is reduced, more time slots are required to send a certain amount of information. Therefore, the amount of information to be sent is also reduced, and the data transmission capacity is only about 1/16-1/3 of the normal channel data transmission capacity. The special channel should preferably only be used to send data required for data connection establishment. In other words, after the connection is established, packet transmission uses the normal channel. In this way, since the position of the user terminal relative to the base station is known, directional antenna beams can be used. Another way to implement packet transmission is to still use a special channel for packet transmission after the connection is established. As mentioned above, the average transmission power of the special channel is the same as that of the common carrier. One embodiment involves only using a special channel, such as a special PRACH channel, in the uplink connection during connection establishment, and completing the signaling required for the downlink connection on a common channel, such as the PAGCH channel. This is possible because after receiving a connection establishment request from a user terminal 102, the network part 100 knows the location of the user terminal, so the network part 100 can use directional antenna beams in its transmissions to the user terminal 102.

Connection establishment here also refers to the control operations performed during the connection. Between successive packets of the same user, the position of the user terminal 102 can change so radically that the previous data for the antenna beam direction can no longer lead to a successful packet transmission. This in turn requires a method of the present invention wherein the network part 100 can detect the orientation of the user terminal 102 relative to the transceiver.

Let us now examine Figure 3. The figure shows a 51 multiframe for the GSM system using the packet radio system. The RACH channel is transmitted in slot 0. Time slots 1-7 are dedicated channels. The traffic channel in time slot 2 is dedicated to the packet radio system and is used to transmit the PRACH channel. According to the present invention, a special channel is established as shown in FIG. 4 . The contents of the remaining time slots 0, 1, 3, 4, 5, 6 and 7 are sent on another normal carrier. The PRACH channel is extended to all time slots in the time domain, since the frequency band of this channel is now narrower and its data transmission rate is lower in the aforementioned manner. Corresponding operations are naturally performed on the downlink.

According to the invention, encoding ensures high gain on a particular channel. This coding ensures that when the connection is established, even special channels containing errors can be received outside the normal channel range, and the originally transmitted information can be correctly decoded based on effective error correction coding and interleaving. For example, in a packet wireless system using CDMA (Code Division Multiple Access) technology, the special channel is spread by its own spreading code and effectively coded. In the CDMA system, the user's narrowband data signal is multiplied by a frequency band A spreading code that is much wider than the data signal, thereby spreading over a relatively wide frequency band. Multiplication enables the data signal to be spread over the entire available frequency band. Each connection between the network part and the user terminal has its own spreading code, which enables the receiver to distinguish the users' signals based on each user's spreading code. Therefore, each user can transmit simultaneously on the same frequency band. Another solution is to send less information on special channels where the spreading rate is more favorable, thus ensuring error-free reception of the transmitted information. The described more efficient coding and reduced amount of transmitted information is naturally also applicable to other multiple access systems (eg FDMA, TDMA) and to systems formed by different combinations of these systems.

The special channel of the present invention can also be established by combining different methods so that the range of the special channel is longer than that of the normal channel. Combining, for example, the per se known increase in transmission power, the described more efficient coding and the change in bandwidth provides the solution according to the invention. Choose the combination that best suits your primary environment.

Let us now examine Figure 5, which shows an example of how the desired scheme of the present invention can be accomplished. According to FIG. 1 , the essential parts of the system are the network part 100 and the user terminals 102 , as well as the intermediate wireless connection 104 . The network part includes base stations, base station controllers and mobile switching centers. Let us examine Figure 5, which illustrates by way of example how the system performs the necessary processing. The base station controller 500 communicates with the base station 510 . Base station controller 500 includes a group switching network 502 , transcoder 504 and control unit 506 . Packet switching network 502 is used to switch voice, data and packets, and to connect signaling circuits. Transcoder 504 converts between and makes compatible the different digital forms of speech coding used by the public switched telephone network and the mobile telephone network. The control unit 506 completes call control, mobility management, collection of statistical data and signaling. The base station 510 includes a frame unit 512 , a frequency hopping unit 514 , a carrier unit 516 and an antenna 518 . In the frame unit 512, channel coding, channel interleaving, data encryption and burst generation are performed. In the frequency hopping unit 514, frequency hopping is optionally performed to a baseband carrier. Modulation and A/D conversion of the transmission signal are performed in the carrier unit 516 . User terminal 102 includes antenna 520 , duplex filter 522 , transmitter 524 and control means 526 . Transmitter 524 includes modulator 530 , channel encoder 532 , scrambler 534 and source encoder 536 .

The base station controller 500 requests the base station 510 to send a connection establishment message to the user terminal 102, for example on the PPCH channel of the GSM system, to establish a connection to the user terminal 102. Carriers generated in carrier unit 516 contain special channels and are transmitted to user terminal 102 via antenna 518 . The user terminal 102 responds accordingly to the connection setup message eg on the PRACH channel in the GSM system. The carrier generated in the modulator 530 contains a special channel, said carrier is sent to the base station 510 . The receivers of base station 510 and user terminal 102 have not been included in the preceding description since they are not essential to the description. The simplest form of implementing the invention is to transform the steps of the method of the invention so that they can be executed by software. Then, the software can be placed, for example, in the memory of the control section 506 of the base station controller 500 . The control section 506 then signals the base station 510 to ensure that the required data in the frame unit 512 is placed on the transmit channel. The carrier unit 516 is also signaled on which frequency it must transmit the particular channel. This scheme can also be implemented with general purpose processors, signal processors or discrete logic. The functions between the base station controller 500 and the base stations may be divided in another manner within the spirit of the invention. The software of the user terminal can be stored in the memory of the control part 526 , and the storage process can be performed in the control part 526 . In this case, software controls the operation of the transmitter 524 , and in particular the operation of the modulator 530 . The scheme can also be implemented with general purpose processors, signal processors or discrete logic.

Although the present invention has been described above with reference to the examples shown in the accompanying drawings, it is obvious that the present invention is not limited thereto, and can be improved in various ways within the scope of the innovative ideas disclosed in the appended claims.

Claims (23)

1. A packet radio system employing SDMA, said system comprising a network part (100), at least one user terminal (102), and a two-way radio connection (104) between the network part (100) and the user terminal (102) , the two-way wireless connection (104) is used for connection establishment and packet transmission, characterized in that, during the connection establishment process, the network part (100) establishes a special channel (210), whose range is much larger than the ordinary channel (200). 2. The system according to claim 1, characterized in that the bit energy-to-noise ratio of the special channel (210) is 5-12 decibels better than that of the normal channel (200). 3. The system according to claim 1, characterized in that the data transmission capacity of the special channel (210) is about 1/16-1/3 of the data transmission capacity of the common channel (200). 4. A system according to claim 1, characterized in that the average transmission power of the special channel (210) is the average transmission power of the normal channel (200). 5. The system according to claim 1, characterized in that the bandwidth of the special channel (210) is far narrower than that of the common channel (200), approximately 1/16-1/3 of the bandwidth of the common channel (200). 6. A system according to claim 1, characterized in that the encoding ensuring high gain is performed on a special channel (210). 7. A system according to claim 1, characterized in that the network part (100) uses the normal channel (200) for packet transmission after the connection is established. 8. A system according to claim 1, characterized in that the network part (100) uses a special channel (210) for packet transmission after connection establishment. 9. A packet radio system employing SDMA, said system comprising a network part (100), at least one user terminal (102), and a two-way radio connection (104) between the network part (100) and the user terminal (102) , the two-way wireless connection (104) is used for connection establishment and packet transmission, characterized in that, during the connection establishment process, the user terminal (102) establishes a special channel (210), whose range is much larger than the ordinary channel (200). 10. The system according to claim 9, characterized in that the bit energy-to-noise ratio of the special channel (210) is 5-12 dB better than that of the normal channel (200). 11. The system according to claim 9, characterized in that the data transmission capacity of the special channel (210) is about 1/16-1/3 of the data transmission capacity of the common channel (200). 12. A system according to claim 9, characterized in that the average transmission power of the special channel (210) is the average transmission power of the normal channel (200). 13. The system according to claim 9, characterized in that the bandwidth of the special channel (210) is far narrower than that of the common channel (200), about 1/16-1/3 of the bandwidth of the common channel (200). 14. A system according to claim 9, characterized in that the encoding ensuring a high gain is performed on a special channel (210). 15. The system according to claim 9, characterized in that the user terminal (102) uses the normal channel (200) for packet transmission after the connection is established. 16. A system according to claim 9, characterized in that the user terminal (102) uses a special channel (210) for packet transmission after the connection is established. 17. A method for establishing a channel in a packet radio system employing SDMA, said packet radio system comprising a network part (100), at least one user terminal (102), and between the network part (100) and the user terminal (102) Two-way wireless connection (104), described two-way wireless connection (104) is used for connection establishment and packet transmission, it is characterized in that, this method comprises the following steps: A) During the establishment of the connection, a special channel (210) is established whose range is much larger than that of the common channel (200). 18. The method according to claim 17, characterized in that the bit energy-to-noise ratio of the special channel (210) is 5-12 dB better than that of the normal channel (200). 19. The method according to claim 17, characterized in that the data transmission capacity of the special channel (210) is about 1/16-1/3 of the data transmission capacity of the normal channel (200). 20. A method according to claim 17, characterized in that the average transmission power of the special channel (210) is the average transmission power of the normal channel (200). 21. The method according to claim 17, characterized in that the bandwidth of the special channel (210) is far narrower than that of the common channel (200), approximately 1/16-1/3 of the bandwidth of the common channel (200). 22. The method as claimed in claim 17, characterized in that the encoding ensuring high gain is performed on a special channel (210). 23. The method according to claim 17, characterized in that the method comprises the steps of: B) After the connection is established, use the special channel (210) for packet transmission.

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