Dtx不连续发射

E User Description, DTX User Description, DTX ©Ericsson Radio Systems AB 7/1553-HSC 103 12 Uen A 1997-09-05 1 (11)©Ericsson Radio Systems AB User Description, DTX 2 (11) 7/1553-HSC 103 12 Uen A 1997-09-05 ©Ericsson Radio Systems AB User Description, DTX Contents 1 Feature overview........................................................................................... 5 1.1 Introduction.............................................................................................. 5 1.2 Background.............................................................................................. 5 1.3 What can be achieved............................................................................. 5 2 Technical description................................................................................... 7 2.1 General .................................................................................................... 7 2.2 Influenced features.................................................................................. 7 2.3 Main differences from Ericsson’s GSM Systems R6.1 ........................... 8 3 Parameters..................................................................................................... 9 3.1 Main controlling parameters.................................................................... 9 3.2 Additional parameters.............................................................................. 9 3.3 Value ranges and default values............................................................. 9 4 References.....................................................................................................11 7/1553-HSC 103 12 Uen A 1997-09-05 3 (11)©Ericsson Radio Systems AB User Description, DTX This page is intentionally left blank 4 (11) 7/1553-HSC 103 12 Uen A 1997-09-05 ©Ericsson Radio Systems AB Feature overview 1 Feature overview 1.1 Introduction If nothing is said into the microphone, there is no point sending anything at all in the air. When the Discontinuous Transmission (DTX) feature is used, the system only transmits when speech is detected over the connection. This decreases the power consumption in the mobile station (MS) and in the Base Tranceiver Station (BTS) and reduces the amount of energy emitted into the air. The DTX feature is implemented in the Base Station Controller (BSC). 1.2 Background During a normal conversation, the participants alternate so that each is silent for about 50% of the time. If the transmitter is silent while there is nothing to be sent, the power consumption in the mobile station is decreased as well as the amount of emitted radio power. Less radio power generates less interference. Since the power level used when transmitting is unaffected, the Carrier-to-Interference ratio (C/I) will be raised for all connections when using DTX. The purposes of the DTX feature are to decrease MS and BTS power consumption and to reduce the overall interference in the system. DTX only affects transmission of Traffic Channel (TCH) frames. 1.3 What can be achieved Discontinuous transmission is a mechanism that allows the radio transmitter to be switched off during speech pauses. In a normal conversation this will lead to a decrease in transmission time of about 50%. DTX is available for speech as well as for non transparent data transmission. It is not used on a Broadcast Control Channel (BCCH) carrier. DTX is available on a per cell basis. The primary functions of DTX in the uplink and downlink are: • uplink - to save battery in the mobile station, - to reduce the interference in the system. • downlink - to reduce the interference in the system, - to decrease BTS power consumption, especially during periods when the BTS is battery operated due to malfunction in the power supply, - to reduce the intermodulation products. When downlink DTX is used in conjunction with uplink DTX, there is an improvement in the C/I ratio in the system. This improvement can be utilised for a tighter cell planning, especially when frequency hopping is used, which means that a higher capacity can be achieved. 7/1553-HSC 103 12 Uen A 1997-09-05 5 (11)©Ericsson Radio Systems AB Feature overview Measurements of the signal strength and the signal quality on the established connection are performed by the mobile station and by the base station. When using DTX, these measurements cannot be performed as often as normal. This disadvantage results in less accurate measurement reports to other radio network features (see also Section 2.2 on page 7 ). Another disadvantage is that the quality of plosives (sounds like "p", "t" and "k") may be a bit poorer, due to the slow response of the Voice Activity Detector (VAD). 6 (11) 7/1553-HSC 103 12 Uen A 1997-09-05 ©Ericsson Radio Systems AB Technical description 2 Technical description 2.1 General The VAD in the transmitter BTS or MS detects whether a traffic frame consists of speech, non transparent data or of background noise. If a frame consists of only noise, the transmitter sends one Silence Descriptor (SID) frame, and then the transmission is stopped. After that, one new SID frame is sent each SACCH period, until speech or non transparent data is detected again. The measurement reports are sent as usual on the SACCH. A SID frame contains information about the background noise of the established connection. In the receiver (MS or BTS) a SID frame detector checks all incoming frames. The detector is able to separate SID frames from speech or non transparent data frames. When a SID frame is detected, the comfort noise characteristics will be updated and comfort noise will be generated. The noise generation is stopped when a speech frame is detected. SID frames are sent for two reasons: to update the comfort noise characteristics on the receiving side and to allow signal strength and signal quality measurements to be made. The VAD must be operating at all times to assess whether the input signal contains speech/non transparent data or not. The MSand/or the BTS sends information in the Measurement Report/ Result, every 480 ms, telling whether it has used DTX some time during that interval or not. 2.2 Influenced features When DTX is used the measurements of signal strength, signal quality and time alignment will be less accurate. Therefore, features using these measurements will be affected, e.g. Dynamic MS Power Control, see ref. 2 page 11and Dynamic BTS Power Control, see ref. 4 page 11 and Locating, see ref. 1 page 11. However, the effect is considered negligible. The Measurement Report consists of two different sets of measurements. One set is based on all 104 TDMA frames, the full set of measurements. The other one is based on the subset of TDMA frames where the SID and SACCH frames are sent (12 TDMA frames, see also ref. 1 page 11). Which set that is selected depends on: • uplink DTX information provided by the MS is checked. If the mobile has been using DTX some time during the measurement period, the subset of measurements will be selected. • downlink The full set of measurements is used if the base station confirms that it is not using DTX. 7/1553-HSC 103 12 Uen A 1997-09-05 7 (11)©Ericsson Radio Systems AB Technical description After a handover to a new base station the subset of measurements is used until a certain number of Measurement Reports has arrived. The required number of reports is set by parameter DTXFUL (see ref. 2). After DTXFUL number of Measurement Reports, the normal criteria described above are used to choose between the full set and subset of measurements. If DTX is used in combination with cyclic frequency hopping, see ref. 3 page 11, hopping when (N) mod 13 = 0 should be avoided, where N is the number of hopping frequencies. This is because all SACCH frames would then be sent on the same frequency. 2.3 Main differences from Ericsson’s GSM Systems R6.1 No changes from Ericsson’s GSM Systems R6.1. 8 (11) 7/1553-HSC 103 12 Uen A 1997-09-05 ©Ericsson Radio Systems AB Parameters 3 Parameters 3.1 Main controlling parameters DTXU is the uplink parameter and states whether the mobile stations located in that cell may (DTXU=0), shall (=1) or shall not (=2) use discontinuous transmission. It is defined per cell. DTXD is the downlink parameter and states whether discontinuous transmission is enabled or not in the cell. This applies for all TCHs allocated on the non BCCH carriers in that cell, for both speech and non transparent data. It is defined per cell. 3.2 Additional parameters DTXFUL defines the number of mesurement reports required to choose the full set of measurements. 3.3 Value ranges and default values Parameter name Default value Recommended value Value range Unit DTXU 2 1 0, 1, 2 DTXD OFF OFF ON, OFF DTXFULL 5 0-40 SACCHperiod 7/1553-HSC 103 12 Uen A 1997-09-05 9 (11)©Ericsson Radio Systems AB Parameters This page is intentionally left blank 10 (11) 7/1553-HSC 103 12 Uen A 1997-09-05 ©Ericsson Radio Systems AB References 4 References 1 User Description, Locating, 3/1553-HSC 103 12 Uen 2 User Description, Dynamic MS Power Control, 5/1553-HSC 103 12 Uen 3 User Description, Frequency Hopping, 8/1553-HSC 103 12 Uen 4 User Description, Dynamic BTS Power Control, 6/1553-HSC 103 12 Uen 7/1553-HSC 103 12 Uen A 1997-09-05 11 (11)©Ericsson Radio Systems AB