WO2005086442A1

WO2005086442A1 - Multi-carrier receiver and method for multi-carrier signal receiving

Info

Publication number: WO2005086442A1
Application number: PCT/CN2004/000186
Authority: WO
Inventors: Alireza Nejatian
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2004-03-08
Filing date: 2004-03-08
Publication date: 2005-09-15

Abstract

Disclosed is a multi-carrier receiver for receiving and processing multi-carrier signals. The receiver comprises a Radio Frequency (RF) part for receiving and processing RF signals; a mixer for down converting the RF signals to Intermediate Frequency (IF) signals; an IF part for filtering and amplifying the IF signals, and an Analogue to Digital Converter (ADC) part for converting the analogue signals to digital signals. The RF part, the mixer, the IF part and the ADC part are connected serially. The IF part includes multiple sets of channel filters for attenuating unwanted signals and interferences around the wanted signal and Variable Gain Amplifiers (VGAs) for amplifying the wanted signal outputted from the channel filters. In addition, different channel filters have different center frequencies respectively corresponding to each signal, and different VGAs have different amplifying gains for amplifying the inputted signal to full scale of ADC. A method for multi-carrier signal receiving is also provided in the invention.

Description

Multi-Carrier Receiver and Method for Multi-Carrier Signal Receiving

Field of the Technology

The present invention relates to multi-carrier signal receiving in mobile communication system, and more particularly to a multi-carrier receiver and a method for multi-carrier signal receiving.

Background of the Invention

As application of communication services has spread rapidly in recent years, the requirement for capacity of system has been increasing. In order to increase the capacity of communication system, multi-carrier technology has been developed. In multi-carrier technology, theoretically N carriers are allowed, wherein N is an integer and bigger than one. But in practice, there are many factors that limit the number of carriers. For example, in a Wideband Code Division Multiple Access (WCDMA) system, there are four adjacent carriers due to spectrum limited for operators. At present, many devices and methods are employed in multi-carrier environment, such as multi-carrier receiver for receiving and processing multi-carrier signals. In order to detect a wanted signal or a plurality of wanted signals in a multi- carrier receiver, a reliable receiver chain or chains are needed. As shown in Fig.l in which a schematic structure diagram of a multi-carrier receiver according to the prior art is illustrated, a multi-carrier receiver comprises a Radio Frequency (RF) part 101 for receiving and processing RF signals, a mixer 102 for down converting the RF signals to Intermediate Frequency (IF) signals, an IF part for filtering and amplifying the IF signals and an analogue to digital conversion part, i.e. Analogue to Digital Converter (ADC) 106, for converting the analogue signals to digital signals for processing in the digital domain. In detail, the IF part at least comprises a channel filter 103 and a Variable Gain Amplifier (VGA) 104. Preferably, the IF part further comprises an anti alias filter 105. Here, the channel filter 103 is responsible for attenuating unwanted signals and interferences around the wanted signal, the VGA 104 is responsible for amplifying the strongest signal among all signals to the full scale of the ADC 106, and the anti alias filter 105 is responsible for down converting the IF signals to those with lower frequency in case of double down conversion, which is very normal at present. Referring to Fig.l again and taking dual carriers as example, the signals FI and F2 transmitted via a communication system are received by the RF part 101 of the multi-carrier receiver firstly. Then, the signals after pre-processing in the RF part 101 go through the mixer 102 for down conversion to IF signals. The IF signals then pass through the channel filter 103 to attenuate the unwanted signals and interferences around the wanted signal. The VGA 104 then amplifies the signals FI and F2. Consequently, the amplified signals are sent to the ADC 106 for analogue to digital conversion. At last, the converted digital signals are sent to digital domain for further processing. One of the key components in a multi-carrier receiver chain is ADC. As is explained before, an ADC is responsible for sampling the inputted IF signals to deliver digital signals for processing in the digital domain. The ADC needed in a multi-carrier receiver should have enough dynamic range and speed for signal processing. In operation, it is desired to use ADC in full scale. Taking dual carriers as example again, the difference between the two signals is as big as 63 dB according to 3 GPP specifications. When the two signals pass through the channel filter, they should be amplified to full scale of ADC. This means the ratio between signals is as before and the strongest signal decides the full scale. Accordingly, in order to have the ability of sampling both signals, the ADC must have enough dynamic range for compensate the difference between the signals. For example, in the case of dual carriers, an ADC with 14 bits or 12 bits is needed. But in practice, there is restriction to buy ADC with 14 bits, and ADC with 12 bits cannot be used outside China, which limits the development of the multi-carrier receiver. So, ADC with lower bits is specially desired.

Summary of the Invention

Accordingly, an object of the present invention is to provide a multi-carrier receiver which has lower number of bits. Another object of the invention is to provide a method for multi-carrier signal receiving. A multi-carrier receiver according to the invention comprises: a Radio Frequency (RF) part for receiving and processing RF signals; a mixer for down converting the RF signals to Intermediate Frequency (IF) signals; an IF part for filtering and amplifying the IF signals, including multiple passes for separating the IF signals and respectively amplifying each IF signal to full scale of ADC; and an Analogue to Digital Converter (ADC) part for converting the analogue signals to digital signals; wherein the RF part, the mixer, the IF part and the ADC part are connected serially In the above-mentioned receiver, the IF part comprises multiple sets of channel filters for attenuating unwanted signals and interferences around the wanted signal and Variable Gain Amplifiers (VGAs) for amplifying the wanted signal outputted from the channel filters, different channel filters have different center frequencies respectively corresponding to each signal, and different VGAs have different amplifying gains for respectively amplifying the inputted signals to full scale of ADC. In the above-mentioned receiver, the ADC part may comprise the same number of ADCs as that of VGAs, and all ADCs have the same structure and are connected to the VGAs serially respectively. In addition, the IF part can further comprise the same number of anti alias filters as that of VGAs, wherein the ADC part comprises the same number of ADCs as that of VGAs and all ADCs have the same structure, each anti alias filter is connected between each VGA and each ADC. In the above-mentioned receiver, the ADC part may comprise an ADC and an adder connected serially, the adder which is responsible for gathering the IF signals is connected to all VGAs. In addition, the IF part further comprise the same number of anti alias filters as that of VGAs, wherein the ADC part comprises an ADC and an adder connected serially, the adder which is responsible for gathering the IF signals is connected to all anti alias filters. In the above-mentioned receiver, the number of the sets of channel filters and VGAs is the same as that of the IF signals. A method for multi-carrier signal receiving according to the invention comprises: a. receiving and processing RF signals in a RF part, then implementing mixing processing for the RF signals, thereby generating IF signals; b. separating the IF signals and amplifying each IF signal to full scale of ADC respectively; and c. implementing analogue to digital conversion for the IF signals and sending the obtained digital signals to a digital domain. In the above-mentioned method, the IF signals are separated through different channel filters having different center frequencies respectively corresponding to each IF signal. In the above-mentioned method, each IF signal is respectively implemented analogue to digital conversion and then sent to the digital domain in step c. Alternately, step c further comprises gathering all amplified signals before implementing analogue to digital conversion, wherein all amplified signals are implemented analogue to digital conversion together in the same ADC and then sent to the digital domain simultaneously. In the above-mentioned method, step b further comprises the step of implementing anti alias filtering for each of the amplified IF signals respectively. It can be seen that there are multiple passes for the IF signals after mixing processing and each pass includes a channel filter and a VGA in the invention. The channel filters and VGAs in different passes have different center frequencies and amplifying gains respectively. In this way, each signal can be filtered and amplified independently, so each signal can be amplified to full scale of ADC. Due to the independency, it is not necessary for the ADC to have more bits to compensate the difference between multiple signals. Accordingly, compared with the prior art, the ADC with lower bits can be used in the present invention. Thus, the complication of device is reduced and the performance is improved.

Brief Description of the Drawings

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: Fig.1 is a schematic structure diagram of a multi-carrier receiver according to the prior art; Fig.2 is a schematic structure diagram of a multi-carrier receiver according to the first embodiment of the invention; Fig.3 is a schematic structure diagram of a multi-carrier receiver according to the second embodiment of the invention; and Fig.4 is a flowchart of the method for multi-carrier signal receiving according to the invention.

Detailed Description of the Invention

Preferred embodiments of the present invention will be described herein below with reference to the accompanying drawings, wherein the same components or parts thereof will be represented with the same reference numerals or symbols to avoid any redundancy or repetition, if available. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. The idea of the present invention is that the IF signals after mixing processing by the mixer are separated and divided to different passes, while the different signals have the same pass in the prior art. In the present invention, each signal has a single pass which at least comprises a channel filter and a VGA. The channel filters in different passes have different center frequencies which correspond to the wanted signals; thereby the wanted signals can be separated from other signals. These signals in different passes are amplified to full scale of ADC respectively. In other words, different VGAs have different amplifying gains. Accordingly, the levels of these signals are independent of each other. Due to the independency, the ADC with lower bits can be employed. Referring to Fig.2 now, Fig.2 illustrates the structure of a multi-carrier receiver according to the first embodiment of the present invention, in which the different signals have their own ADCs. In the first embodiment, the multi-carrier receiver comprises a RF part, a mixer, an IF part and an ADC part. Here, the IF part includes multiple sets of channel filters and VGAs, meanwhile the ADC part include a plurality of ADCs. The number of the sets of channel filters and VGAs is the same of the number of the ADCs, which also is the same as the number of signals. Taking dual carriers as example which is illustrated in Fig.2, there are two sets of channel filters and VGAs and two ADCs corresponding to the two signals FI and F2. In other words, there are two passes for the two signals after mixing processing and each pass at least includes a channel filter, a VGA and an ADC. Preferably, each pass further include an anti alias filter. In detail, the multi-carrier receiver according to the first embodiment comprises a RF part 101, a mixer 102, two channel filters 203, 203', two VGAs 204, 204', two anti alias filters 205, 205' and two ADCs 206, 206'. The RF part 101 which is responsible for receiving and processing RF signals is connected to the mixer 102 for down converting the RF signals to IF signals. A channel filter 203, a VGA 204, an anti alias filter 205 and an ADC 206 are connected serially, while the other channel filter 203', the other VGA 204', the other anti alias filter 205' and the other ADC 206' are connected serially. Both the two channel filters 203, 203' are connected to the mixer 102. In this embodiment, the signals FI and F2 are received by the RF part 101 and sent to the mixer 102 after the processing in the RF part 101. After mixing processing in the mixer 102, the signals FI and F2 are sent to two passes. That is, the signals are sent to both of the channel filters 203 and 203' which have different center frequencies in accordance with the different signals. For signals FI and F2, the channel filter 203 has the center frequency corresponding to the signal FI while the channel filter 203' has the center frequency corresponding to the signal F2. As is explained before, the difference between the two signals is 63 dB, thus the signal FI can pass the channel filter 203 and cannot pass the channel filter 203'. In similar, the signal F2 cannot pass the channel filter 203 but can pass the channel filter 203'. In this way, the two signals FI and F2 are separated by different channel filters and divided to different passes. After the channel filtering processing, the signal FI is sent to the VGA 204 and the signal F2 is sent to the VGA 204'. In order to amplify the two signals with different levels to the same full scale of ADC, the amplifying gains of the two VGAs 204 and 204' are different. For example, the signal FI is stronger than F2, so the amplifying gain of the VGA 204' is greater than that of the VGA 204. After amplifying processing in the VGAs 204 and 204', the signals FI and F2 have the same or almost the same levels, referring to the Fig.2. Then, the two signals with the same or almost the same levels are sent to the ADCs 206 and 206' respectively. Since only one signal needs to be processed in one ADC, it is not necessary for the ADC to have more bits to compensate the difference between multiple signals. Accordingly, compared with the prior art, the ADC with lower bits can be used in the present invention. Referring to Fig.3 now, Fig.3 illustrates the structure of a multi-carrier receiver according to the second embodiment of the present invention, in which the different signals have the same ADC. The RF part, mixer and IF part in the second embodiment is the same as that in the first embodiment, so the detail description about them will be omitted hereinafter, and only the difference between the two embodiments will be described in detail. In the second embodiment, the ADC part includes only one ADC, but further includes an adder. After anti alias filtering, the signals FI and F2 are sent to an adder 307 which is responsible for gathering the signals. Then, the signals FI and F2 are gathered and sent to the ADC 306 through the same pass. Since the signals FI and F2 have been amplified to the same or almost the same scale of ADC 306 in the IF part, the ADC need not have more bits to compensate the difference between multiple signals also. Like the first embodiment, compared with the prior art, the ADC with lower bits can be used in this embodiment of the present invention. According to the multi-carrier receiver of the invention, a method for multi- carrier signal receiving is also provided in the invention. The method comprises the following steps. In step 401, the RF signals are received and processed by the RF part. Then, the processed signals are sent to the mixer for down conversion to IF signals. The IF signals are sent to a plurality of channel filters which have different center frequencies corresponding to the different signals in the same time. In step 402, the IF signals are separated. In detail, through adjusting the center frequency of the channel filter be the same as the frequency of the wanted signal, the multiple channel filters respectively filter the signals and make the wanted signal pass through it and other signals be discarded. In step 403, the VGAs in different passes respectively amplify the wanted signal to full scale of ADC. Since the levels of different signals are different and the full scale of ADC is the same, the amplifying gains of different VGAs are different in relation to the different levels of signals. In step 404, the anti alias filters in different passes respectively implement anti alias filtering for the signals outputted from the VGAs. In step 405, the signals with the same or almost the same levels are sent to the ADC part for analogue to digital conversion. Here, the signals can be sent to multiple ADCs respectively, or can be sent to an adder for gathering and the gathered signals are sent to the same ADC. In step 406, the digital signals are sent to the digital domain for further processing. In the method, since the signals sent to the ADC part have the same or almost the same levels, the ADC need not have more bits to compensate the difference between multiple signals. Accordingly, the ADC with lower bits can be used. The above-mentioned multi-carrier receiver and the method are adapted to be used specially in WCDMA system. In addition, the invention is suitable for all kind of receiving architecture, dual down conversion, single conversion or other types. So, although the invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example, and is not to be taken by way of limitation. The spirit and scope of the present invention are to be limited only by the terms of the appended claims.

Claims

1. A multi-carrier receiver for receiving and processing multi-carrier signals, comprising: a Radio Frequency (RF) part for receiving and processing RF signals; a mixer for down converting the RF signals to Intermediate Frequency (IF) signals; an IF part for filtering and amplifying the IF signals, including multiple passes for separating the IF signals and respectively amplifying each IF signal to full scale of ADC; and an Analogue to Digital Converter (ADC) part for converting the analogue signals to digital signals; wherein the RF part, the mixer, the IF part and the ADC part are connected serially.

2. The multi-carrier receiver of claim 1, wherein the IF part comprises multiple sets of channel filters for attenuating unwanted signals and interferences around the wanted signal and Variable Gain Amplifiers (VGAs) for amplifying the wanted signal outputted from the channel filters, different channel filters have different center frequencies respectively corresponding to each signal, and different VGAs have different amplifying gains for respectively amplifying the inputted signals to full scale of ADC.

3. The multi-carrier receiver of claim 2, wherein the ADC part comprises the same number of ADCs as that of VGAs, and all ADCs have the same structure and are connected to the VGAs serially respectively.

4. The multi-carrier receiver of claim 2, further comprising the same number of anti alias filters as that of VGAs, wherein the ADC part comprises the same number of ADCs as that of VGAs and all ADCs have the same structure, each anti alias filter is connected between each VGA and each ADC.

5. The multi-carrier receiver of claim 2, wherein the ADC part comprises an ADC and an adder connected serially, the adder which is responsible for gathering the IF signals is connected to all VGAs.

6. The multi-carrier receiver of claim 2, further comprising the same number of anti alias filters as that of VGAs, wherein the ADC part comprises an ADC and an adder connected serially, the adder which is responsible for gathering the IF signals is connected to all anti alias filters.

7. The multi-carrier receiver of any one of claims 2 to 6, wherein the number of the sets of channel filters and VGAs is the same as that of the IF signals.

8. A method for multi-carrier signal receiving, comprising: a. receiving and processing RF signals in a RF part, then implementing mixing processing for the RF signals, thereby generating IF signals; b. separating the IF signals and amplifying each IF signal to full scale of ADC respectively; and c. implementing analogue to digital conversion for the IF signals and sending the obtained digital signals to a digital domain.

9. The method of claim 8, wherein the IF signals are separated through different channel filters having different center frequencies respectively corresponding to each IF signal.

10. The method of claim 8, wherein in step c, each IF signal is respectively implemented analogue to digital conversion and then sent to the digital domain.

1 1. The method of claim 8, step c further comprising gathering all amplified signals before implementing analogue to digital conversion, wherein all amplified signals are implemented analogue to digital conversion together in the same ADC and then sent to the digital domain simultaneously.

12. The method of claim 8, step b further comprising the step of implementing anti alias filtering for each of the amplified IF signals respectively.