HK1192669A

HK1192669A - Power level of transmitted control channel symbol

Info

Publication number: HK1192669A
Application number: HK14105837.0A
Authority: HK
Inventors: Cozzo Carmela; BJÖRKEGREN Håkan; Edholm Christer; Bergman Johan
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2006-12-21
Filing date: 2014-06-19
Publication date: 2014-08-22

Description

Power level of transmitted control channel symbols

Technical Field

The present invention relates generally to channel estimation and, more particularly, to adjusting the power level of a physical control channel so that symbols received on the physical control channel can be reliably used to perform channel estimation regardless of a data transmission rate.

Background

In a wireless communication network, if a receiver can accurately estimate a channel, i.e., a signal propagation path between the receiver and a transmitter, communication accuracy between the receiver and the transmitter increases. Channel estimation is typically based at least in part on recovering known pilot symbols. For the uplink, the Universal Mobile Telecommunications System (UMTS) specifies a Dedicated Channel (DCH) and an enhanced dedicated channel (E-DCH), both of which correspond to a set of independent channelization codes and associated control signaling for data. The number of data codes carrying the E-DCH and the spreading factor depend on the used data rate. The E-DCH dedicated physical data channel (E-DPDCH) carries the E-DCH transport channel. An E-DCH dedicated physical control channel (E-DPCCH) carries control information associated with the E-DCH. In particular, the E-DPCCH carries information of a transport block format (e.g., E-TFCI symbols), information for hybrid automatic repeat-request (ARQ) and scheduling. The control channel E-DPCCH carries pilot and control symbols. The E-DPDCH and E-DPCCH channels may be multiplexed with data channels (DPDCHs) of the DCH which use 10ms Transmission Time Intervals (TTIs) for circuit switched traffic.

Higher order modulation schemes and higher data transmission rates are being implemented as part of High Speed Packet Access (HSPA) evolution. Higher order modulation schemes such as 16QAM (quadrature amplitude modulation) and above always result in reduced symbol spacing. Improved channel estimation is needed when higher order modulation schemes are used, because symbol detection becomes more difficult when the signal spacing is reduced. In addition to using the DPCCH symbols for channel estimation, channel estimation accuracy can be improved by using E-DPCCH symbols. At high data rates, the E-DPDCH uses high order modulation and is transmitted at high power. Conventional systems do not change the power level of the DPCCH and E-DPCCH with respect to the data transmission rate. Thus, the symbols transmitted on the DPCCH and E-DPCCH become unreliable when using higher order modulation, since the DPCCH and E-DPCCH symbols will be swamped by the high power E-DPDCH. Also, DPCCH and E-DPCCH cannot be used to obtain accurate channel estimates over a wide range of data transmission rates.

Disclosure of Invention

In accordance with the methods and apparatus taught herein, the power level of a physical control channel assigned to a receiver is adjusted based on the transmission rate and/or transport format of the corresponding physical data channel assigned to the same receiver. In one embodiment, the E-DPCCH power level is adjusted based on the E-DPDCH transmission rate and/or transport format. In another embodiment, the DPCCH power level is adjusted based on the E-DPDCH transmission rate and/or the transport format. The power level of other types of physical control channels may also be modulated accordingly. In any case, the power level of the physical control channel is optimized as a function of the transmission rate and/or the transmission format.

Thus, the receiver can reliably perform channel estimation over a wide range of data transmission rates using control symbols transmitted via at least one of the physical control channels. In one embodiment, the control channel power level is adjusted based on the modulation scheme of the corresponding physical data channel. In another embodiment, the power level of the control channel is adjusted based on the transport block size of the physical data channel. In any event, at high data transmission rates, increasing the power level of the control channel will increase the channel estimation accuracy. This in turn improves demodulation performance at high data streams. The power level of the control channel may be increased to a level that ensures reliable channel estimation. Further increases may result in a decrease in uplink/downlink capacity. At low data rates, the power level of the control channel may be reduced enough to improve uplink/downlink capacity but still remain high enough to constructively aid channel estimation. In addition, adjusting the control channel power level based on the data transmission rate and/or transport format reduces the amount of interference injected into the data channel from the control channel.

In one embodiment, the power level of the physical control channel assigned to the receiver is adjusted based on the transmission rate and/or transport format of the physical data channel assigned to the receiver. The control channel symbols are transmitted to the receiver over the physical control channel at the adjusted power level. The receiver uses the control channel symbols to perform channel estimation.

Of course, the present invention is not limited to the above features and advantages. Those skilled in the art will appreciate still other features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings.

Drawings

Fig. 1 is a block diagram of an embodiment of a receiver including a baseband processor operable to perform channel estimation based at least in part on control channel symbols received from a physical control channel having an adjustable power level.

Fig. 2 is a logic flow diagram of an embodiment of processing logic to perform channel estimation using control channel symbols received from a physical control channel having an adjustable power level.

Fig. 3 is a graph illustrating an embodiment of a physical control channel with adjustable power levels.

Detailed Description

Fig. 1 shows an embodiment of a wireless communication system 100 comprising a wireless base station 102 and a mobile station 104. The wireless communication system 100 supports uplink (mobile station to base station) and downlink (base station to mobile station) communications. The operation of the wireless communication system 100 is described next for uplink communications. However, those skilled in the art will appreciate that the control channel power adjustment embodiments disclosed herein are applicable to both the uplink and downlink directions. Also, as used herein, the term "receiver" refers to both the mobile station 104 for downlink communications and the wireless base station 102 for uplink communications. Similarly, the term "transmitter" is used herein to refer to both the wireless base station 102 for downlink communications and the mobile station 104 for uplink communications.

With this understanding, one or more dedicated channels, e.g., DCHs and/or E-DCHs, are allocated between the mobile station 104 and the radio base station 102 for supporting uplink communications with the mobile station 104. In one embodiment, the E-DPDCH is allocated to carry the E-DCH channel. The corresponding E-DPCCH carries control information to the base station 102. The E-DPDCH and E-DPCCH are multiplexed with DPCCH (and DPDCH) channels of DCHs also allocated between the mobile station 104 and the base station 102. Alternatively, only DCHs are allocated between the base station 102 and the mobile station 104. In another embodiment, other types of physical data and control channels are allocated for supporting downlink/uplink communications.

In any event, the power level of the physical control channel is adjusted between the mobile station 104 and the base station 102 based on the transmission rate and/or transport format of the corresponding data channel, as shown in step 200 of fig. 2. For example, the control channel power level may increase in response to an increase in the transmission rate of the physical data channel. Conversely, the control channel power may be decreased in response to a decrease in the data channel transmission rate. Similarly, the control channel power may be adjusted in response to changes in the transport format of the data channel, such as changes in the modulation scheme and/or transport block size.

If the DPCCH power level is changed, it will have an effect on the received signal-to-interference ratio (SIR) experienced at the base station 102. This in turn affects the power control loop. Thus, the base station 102 adjusts the SIR target of the power control loop. In general, the E-DCH transport format combination identifier (E-TFCI) provides the base station 102 with information regarding the transmitted modulation scheme used at the mobile station 104. The base station 102 uses the E-TFCI to modify the SIR target when performing DPCCH power level adjustment. Adjusting the power level of the E-DPCCH has less impact on the received SIR because the E-DPCCH may be transmitted less frequently than the DPCCH. Despite this nuance associated with the DPCCH, there are various ways to adjust the power level of the DPCCH and any type of physical control channel.

The power level of the physical control channel may be linearly adjusted based on the transmission rate and/or transport format of the corresponding data channel shown in fig. 1. In WCDMA, the E-DPCCH power level is linearly adjusted based on the transport block size of the corresponding E-DPDCH. The E-DPCCH power may be used at a level similar to how the E-DPDCH power level is based on it as described in the 3 rd generation partnership project published document 3GPP TS25.214 "Physical layer reduction (FDD)"The manner in which the transport block size is changed is linearly adjusted. Linearly adjusting the control channel power level based on transport block size will result in an E that ensures that a relatively constant is maintained for all data transmission rates_b/N_oSIR estimation of where E_bFor energy per bit, N_oIs the noise power spectral density. Bit Error Rate (BER) performance is not adversely affected when different transport block sizes and/or modulation schemes are used.

Instead of linearly adjusting the power level of the physical control channel, it may be non-linearly adjusted. In one embodiment, the control channel power is adjusted based on the corresponding physical data channel. Thus, the control channel power may be adjusted in a stepwise or non-linear manner in response to changes in the modulation scheme shown in fig. 3. For example, the control channel may be stepped up or ramped up as the data modulation order increases from QPSK to 16-QAM or higher. When channel condition is guaranteed (warrange), the data channel modulation scheme can then be reduced to a lower capacity modulation scheme in order to reduce channel transmission errors. Accordingly, the control channel power is therefore stepped down or ramped down.

In another embodiment, the power level of more than one physical control channel allocated to the mobile station 104 may be adjusted. In one embodiment, the power levels of the E-DPCCH and DPCCH are adjusted based on the transmission rate and/or transport format of their corresponding data channels. The same or different (e.g., linear/non-linear) functions for different ranges of transport block sizes and/or modulation schemes may be used to adjust each control channel.

After performing the power change, the control channel symbols are transmitted to the radio base station 102 at the adjusted power level on the physical control channel, e.g., as shown in step 202 of fig. 2. The base station 102 uses the control channel symbols to perform channel estimation, e.g., as shown in step 204 of fig. 2. In one embodiment, front-end circuitry 106 filters, down-converts, and digitizes received data and control symbols into corresponding baseband signal streams. The baseband processor 108 extracts control channel symbols from the baseband signal stream. A channel estimator 110 included in or associated with the baseband processor 108 performs channel estimation using the extracted control channel symbols, as is well known in the art. The baseband processor 108 detects and decodes the transmitted data symbols based on the channel estimates and other parameters, such as combining weights, as is well known in the art.

Adjusting the control channel power in accordance with any of the various embodiments described herein improves channel estimation accuracy because symbols received from the control channel can be used to perform channel estimation despite varying data transmission rates, modulation schemes, and/or transport block sizes. At high data rates, the control channel power is increased so that high power symbols are available for channel estimation. Conversely, control channel power is reduced at low data rates so that power is not unnecessarily consumed on the control channel, thereby reducing interference to the data channel. However, control symbols may also be received from the physical control channel and used for channel estimation at low data transmission rates.

With the above range of variations and applications in mind, it should be understood that the present invention is not limited by the foregoing description, nor is it limited by the accompanying drawings. Rather, the invention is limited only by the following claims and their reasonable equivalents.

Claims

1. A method of transmitting symbols for channel estimation, comprising:

-adjusting (200) a power level of a physical control channel allocated to a receiver based on a transmission rate and/or a transport format of a physical data channel allocated to said receiver; and

transmitting control channel symbols to the receiver at the adjusted power level on the physical control channel for use by the receiver in performing channel estimation (202).

2. The method of claim 1, wherein adjusting the power level of the physical control channel comprises adjusting the power level of at least one of a dedicated physical control channel assigned to the receiver and an enhanced dedicated physical control channel assigned to the receiver.

3. The method of claim 1, wherein adjusting the power level of the physical control channel comprises linearly adjusting the power level of the physical control channel based on a transmission rate and/or a transport format of the physical data channel.

4. The method of claim 1, wherein adjusting the power level of the physical control channel comprises adjusting the power level of the physical control channel based on a modulation scheme of the physical data channel.

5. The method of claim 4, wherein adjusting the power level of the physical control channel based on the modulation scheme of the physical data channel comprises gradually adjusting the power level of the physical control channel in response to a change in the modulation scheme of the physical data channel.

6. The method of claim 1, wherein adjusting the power level of the physical control channel comprises adjusting the power level of the physical control channel based on a transport block size of the physical data channel.

7. The method of claim 1, wherein adjusting the power level of the physical control channel comprises:

increasing a power level of the physical control channel in response to an increase in a transmission rate of the physical data channel; and

reducing a power level of the physical control channel in response to a decrease in a transmission rate of the physical data channel.

8. The method of claim 1, further comprising:

adjusting a power level of an additional physical control channel allocated to the receiver based on a transmission rate and/or a transport format of the additional physical data channel allocated to the receiver; and

transmitting additional control channel symbols to the receiver on the additional physical control channel at its adjusted power level for use by the receiver in performing channel estimation.

9. The method of claim 1, wherein transmitting the control channel symbols to the receiver at the adjusted power level on the physical control channel comprises transmitting the control channel symbols to the receiver at the adjusted power level on an uplink physical control channel.

10. A transmitter comprising a baseband processor (108), the baseband processor configured to:

adjusting a power level of a physical control channel allocated to a receiver based on a transmission rate and/or a transport format of a physical data channel allocated to the receiver; and

transmitting control channel symbols to the receiver on the physical control channel at the adjusted power level for use by the receiver in performing channel estimation.

11. The transmitter of claim 10, wherein the baseband processor is configured to adjust a power level of at least one of a dedicated physical control channel assigned to the receiver and an enhanced dedicated physical control channel assigned to the receiver.

12. The transmitter of claim 10, wherein the baseband processor is configured to linearly adjust the power level of the physical control channel based on a transmission rate and/or a transport format of the physical data channel.

13. The transmitter of claim 10, wherein the baseband processor is configured to adjust the power level of the physical control channel based on a modulation scheme of the physical data channel.

14. The transmitter of claim 13, wherein the baseband processor is configured to adjust the power level of the physical control channel in steps in response to changes in the modulation scheme of the physical data channel.

15. The transmitter of claim 10, wherein the baseband processor is configured to adjust the power level of the physical control channel based on a transport block size of the physical data channel.

16. The transmitter of claim 10, wherein the baseband processor is configured to:

17. The transmitter of claim 10, wherein the baseband processor is further configured to:

adjusting a power level of an additional physical control channel allocated to a receiver based on a transmission rate and/or a transport format of the additional physical data channel allocated to the receiver; and

18. The transmitter of claim 10, wherein the baseband processor is configured to transmit the control channel symbols to the receiver on an uplink physical control channel at the adjusted power level.

19. A receiver comprising a baseband processor (108), the baseband processor configured to:

detecting control channel symbols received from a physical control channel assigned to the receiver at a power level corresponding to a transmission rate and/or a transport format of a physical data channel assigned to the receiver; and

channel estimation is performed based at least in part on the detected control channel symbols.

20. The receiver of claim 19, wherein the baseband processor is configured to detect control channel symbols received from at least one of a dedicated physical control channel assigned to the receiver and an enhanced dedicated physical control channel assigned to the receiver.

21. The receiver of claim 19, wherein the baseband processor is further configured to:

detecting control channel symbols received from an additional physical control channel assigned to the receiver at a power level corresponding to a transmission rate and/or a transport format of an additional physical data channel assigned to the receiver; and

performing channel estimation based at least in part on the control channel symbols received from the physical control channel.

22. The receiver of claim 19, wherein the baseband processor is configured to detect control channel symbols received from an uplink physical control channel.

23. A method of performing channel estimation at a receiver, comprising:

detecting (202) control channel symbols received from a physical control channel assigned to the receiver at a power level corresponding to a transmission rate and/or a transport format of a physical data channel assigned to the receiver; and

channel estimation is performed (204) based at least in part on the detected control channel symbols.

24. The method of claim 23, wherein detecting the control channel symbols comprises detecting control channel symbols received from at least one of a dedicated physical control channel assigned to the receiver and an enhanced dedicated physical control channel assigned to the receiver.

25. The method of claim 22, further comprising: