Antenna diversity receiver

Antenna diversity receiver

Technical field

The invention relates to an antenna diversity receiver used in a radio communication system. Although the present invention is specifically described with reference to a Bluetooth system, it is also applicable to other communication system fields in which antenna diversity can be used.

Background technique

Radio communication systems are often affected by multipath propagation, so that the transmitted signal passes from the transmitter to the receiver through many different paths. Each path (except the direct path, if any) is reflected from one or more objects, and thus these paths have different lengths. The signals from all reachable paths are recombined on the antenna and supplied to the receiver. Depending on the instantaneous set of the path length, the received signal can interfere constructively or destructively on the antenna.

In the case of destructive interference, the instantaneous signal strength can be reduced by 20 dB or more compared to the signal strength of the direct path. This problem is particularly serious in systems used indoors. Typically, there are various scattering objects (such as walls, furniture, people) that are placed closely together, some of which are not stationary. In extreme cases, it is impossible for the receiver to receive a signal of sufficient strength for use, and it is considered to be in a state of zero signal.

One solution to this problem is antenna diversity, in which two or more receiving antennas are provided for one receiver. If the antennas are sufficiently separated so that the signal received on one antenna is actually uncorrelated with the signal received by the other antenna, when one antenna is in a zero signal state, the other antenna may be able to receive a good signal.

An example of a radio communication system that can use antenna diversity is the Bluetooth network, which operates in accordance with the technical conditions specified by the Bluetooth Specialized Industry Group. Such a network is intended to provide low-cost, short-distance radio links between mobile PCs, mobile phones, and other portable or not. The communication in the Bluetooth network is carried out in the unlicensed ISM frequency band of approximately 2.45 GHz. At these frequencies, antenna separation on the order of a few centimeters is sufficient for successful diversity operation.

For example, in an antenna diversity receiver disclosed in US-A-5,940,452, the diversity controller selects the antenna that provides the best signal based on the signal quality measurement result, most commonly RSSI (Received Signal Strength Indication). Other channel quality measurements can be used, for example, checksums are used in some cases in DECT (Digital Enhanced Cordless Telecommunications) systems. In a radio communication system where data is sent in groups, it is the best practice for the diversity controller to select the best antenna on a group-by-group basis. This is especially true in frequency hopping systems such as Bluetooth. Because successive packets will be sent on different frequencies with irrelevant characteristics.

However, implementing antenna diversity on a group-by-group basis requires measuring the signal quality from each antenna in turn (unless multiple receivers are provided, which is usually not a practical solution). The sequence used in known receivers is The RSSI measurement process may therefore take too long, especially if the preamble for each packet is relatively short (for example, only 4 μs long in Bluetooth).

Summary of the invention

An object of the present invention is to provide an antenna diversity receiver that can compare the signal quality from two antennas at the same time without requiring multiple receivers.

Specifically, the present invention provides an antenna diversity radio receiver, including: first and second signal paths, a corresponding quadrature correlation mixer for down-converting received signals, and a corresponding down-converter for filtering A channel filtering device for a signal; a demodulation device coupled to the channel filtering device for demodulating the filtered signal; a switching device having first and second input terminals for connecting to corresponding first and second antennas , For receiving signals, and having first and second output terminals coupled to corresponding first and second signal paths, wherein the switching device has a first state, a second state, and a third state, wherein the first In the state, the signal received from the first antenna is routed to the first signal path, and the signal received from the second antenna is routed to the second signal path, and in the second state the signal received from the first antenna is routed To two signal paths, and the signal received from the second antenna in the third state is transmitted to the two signal paths; and the antenna diversity radio receiver further includes a diversity control device, the diversity control device in the switching The device is coupled to the first and second signal paths when in its first state and is suitable for determining the relative quality of the received signals in the first and second signal paths, and the diversity control device is coupled to the switching device and It is suitable for controlling the state of the switching device according to the determined relative signal quality.

According to the present invention, there is provided an antenna diversity receiver including: in-phase and quadrature channels; a device for connecting to first and second antennas; a switching device having a first state, a second state, and a third state, wherein In the first state, the signal from the first antenna is transmitted to the co-channel and the signal from the second antenna is transmitted to the orthogonal channel. In the second state, the signal from the first antenna is transmitted to the co-channel and transmitted To the quadrature channel, and in the third state, the signal from the second antenna is transmitted to both the co-channel and the quadrature channel; the signal quality comparison device is used to determine that it is in the same phase when the switching device is in its first state And the relative quality of the received signal in the orthogonal channel; and the diversity control device for controlling the state of the switching device according to the relative signal quality determined by the signal quality comparison device.

Description of the drawings

The embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a block diagram of a zero IF (intermediate frequency) radio receiver; Figure 2 is the required and adjacent channel signals Figure 3 is a graph of the signal of Figure 2 mixed with zero IF; Figure 4 is a graph of the signal of Figure 3 after channel filtering; and Figure 5 is an antenna diversity zero IF radio receiver made according to the present invention Schematic block diagram.

In the drawings, the same reference numerals are used to indicate corresponding features.

detailed description

A block diagram of a conventional zero-IF receiver is shown in Figure 1. Its operation will be explained by referring to Figs. 2 to 4, which are diagrams showing signals that are received and processed in the receiver. The radio frequency (RF) signal is received by the antenna 102 and amplified by the low noise amplifier (LNA) 104. The RF signal at this level is shown in Figure 2, which is a graph of signal amplitude A versus frequency f. The first frequency band 202 contains the desired signal (W), and the second and third frequency bands 204, 206 contain unwanted adjacent channel signals A1, A2.

The output of the LNA 104 is fed to a pair of quadrature-related mixers 106, 108, which are supplied with in-phase (I) and quadrature (Q) local oscillator (LO) signals, respectively. The LO signal is generated by a voltage controlled oscillator (VCO) 110, and the voltage controlled oscillator is driven by a frequency synthesizer (SYN) 112 with a stable reference signal source 114. The LO signal has the same frequency as the center of the frequency band 202 containing the desired signal, so the mixers 106, 108 mix the signal to a zero frequency, folding the received spectrum around the frequency. The signal is now as shown in FIG. 3, with a low frequency band 302 containing the desired signal folded around the zero frequency, and a high frequency band 304 containing adjacent channel signals A1 and A2 superimposed.

The output signals from the I and Q mixers 106, 108 are then filtered by low-pass I and Q channel filters 116, 118 to attenuate the high frequency band 304. Figure 4 shows the resulting signal with idealized filter characteristics 402 as shown by the dashed line, and the high frequency band 304 has been removed as a result of filtering. The output signals from the channel filters 116, 118 then pass through I and Q limiters 120, 122 before being converted into digital signals by I and Q single-bit analog-to-digital converters (ADC) 124, 126. The limiters 120, 122 remove the amplitude information before input to the ADCs 124, 126. The digital signals are then sent through the frequency discriminator (DISC) 128 to the baseband processing block (BB) 130, where they are demodulated. By using the baseband processing of the I and Q channels, the effect of spectrum folding can be removed.

By adding a switch before the LNA 104 to enable a selection signal from one of the antennas 102, the receiver of FIG. 1 can be modified to operate with two antennas 102 to allow diversity switching. The signal quality indication from each antenna 102 can then be obtained sequentially, for example during a preamble in the transmitted data. Once this measurement has been completed, an antenna that provides a better signal, such as an antenna with a higher RSSI, is selected.

Although such techniques have been used successfully, the fact that only one signal can be received at a time means that the measurement process takes a considerable amount of time. In a DECT system, there are optional provisions for extending the preamble file so that such a measurement process can be completed. However, in a system such as Bluetooth where the preamble file is very short, only 4μs, there is not enough time for such a measurement process. As an alternative, it seems possible to have two separate receivers in order to be able to perform signal quality measurements at the same time, but such a receiver cannot be economically implemented.

The present invention provides a solution to the problem that a single receiver can be used for simultaneous signal quality measurement. The block diagram of the receiver made according to the present invention is shown in FIG. 5. Most of the receiver is the same as the receiver of FIG. 1, so it will not be described again.

The receiver includes first and second antennas 102a, 102b connected to respective first and second LNAs 104a, 104b. The LNAs 104a, 104b are connected to the quadrature associated mixers 106, 108 through first and second dual switches 532, 534. In addition, a diversity controller (DC) 536 is provided to compare the received signal quality and control the switches 532, 534 and the LNA 104a, 104b accordingly. When the two switches 532, 534 are in the'up' position, as shown in FIG. 5, the receiver operates in the same manner as the normal zero IF receiver shown in FIG. 1 to receive the signal from the first antenna 102a. Similarly, when the two switches 532, 534 are in the'down' position, signals are received from the second antenna 102b.

When the first switch 532 is in the'up' position and the second switch 534 is in the'down' position, simultaneous signal quality measurement (or comparison) can be completed. The signal from the first antenna 102a is sent to the I mixer 106, down-mixed to zero frequency and filtered. The resulting signal is folded around zero frequency, as shown in Figure 4, so it cannot be demodulated, but it is still possible to make effective signal strength measurements. Likewise, the signals from the second antenna 102b are sent to the Q mixer 108, and their intensity measurement can be completed after filtering. The fact that the signal from the first antenna 102a is mixed with the in-phase LO signal and the signal from the second antenna 102b is mixed with the quadrature LO signal is not important because it does not affect the measured signal strength.

The diversity controller 536 can compare the signal quality from the two antennas during the preamble file in the transmitted data and determine which antenna 102a, 102b is used for the rest of the data. Therefore, when a decision is made, the switches 532, 534 are set accordingly, and the receiver functions as a normal zero-IF receiver. The LNA 104a, 104b connected to the unused antenna 102a, 102b can be disconnected during data reception, thereby minimizing receiver power consumption.

Compared with the usual zero-IF receiver, the receiver made according to the present invention only needs a small amount of additional circuits (in the embodiment shown, it is an LNA and two switches). Disconnecting the additional LNA during this period only slightly increases the power consumption of the receiver.

Various modifications to the receiver design shown in Figure 5 are possible. For example, the limiters 120, 122 can be eliminated, and the single-bit ADCs 124, 126 are replaced by multi-bit ADCs. Enables signal strength measurements to be made directly from the digital part of the receiver. The basic feature of the receiver made according to the present invention is that two channels (usually I and Q) are required for normal operation, but each channel can transmit different signals during signal quality measurement or comparison.

The embodiment disclosed above is a direct conversion receiver in which the RF signal is directly downmixed to zero frequency. However, the present invention is applicable to other zero-IF structures, such as a two-level down-conversion scheme. It is also suitable for low IF structures using polyphase filters, although implementation with such a structure requires considerable additional circuitry. In particular, it is necessary to obtain signals in each of the I and Q channels between the mixer 106, 108 and the polyphase filter replacing the channel filter 116, 118 of FIG. 5. Then each of these signals needs to pass through a separate channel filter to filter out adjacent channel signals before the signal quality measurement can be performed.

Although the present invention has been described for Bluetooth systems or other systems with very short preamble files, measuring the signal strength from two antennas at the same time has great advantages and can be easily applied to various radio communication systems, such as , UMTS (Universal Mobile Telecommunications System), GSM (Global System for Mobile Communications) or DECT.

Through reading the present disclosure, other modifications will be obvious to those skilled in the art. Such modifications can be included in the design, manufacture, and use of the antenna diversity receiver and other features already known in its component parts, and can replace or supplement other features already described herein. Although the claims have been cooperatively described in this application for a specific group of these characteristics, it should be understood that the scope of the disclosure of this application also includes any new characteristics disclosed herein in an obvious or implicit way or in any general way. Or any combination of new features, regardless of whether it involves the same invention that is currently patented in the claims and whether it alleviates any or all of the same technical problems accomplished by the present invention. The applicant hereby draws attention to the fact that new claims may elaborate on such features and/or combinations of features during the course of this application or any further applications derived therefrom.

In this specification and claims, the word "a" before a component does not exclude the presence of multiple such components. In addition, the word "comprising" does not exclude the presence of other components or steps than those listed.