Patent Application
20080205509
1. Field of the Invention
The present invention relates to a method for the simultaneous wireless transmission of a video stream or streams and high-speed data in a domestic environment. It also relates to a terminal for the simultaneous transmission of a video stream or streams and high-speed data. More specifically, it applies to a framework in which the IEEE 802.11abg (Wi-Fi) WLAN standards and the emerging 802.11n standard are implemented.
2. Description of the Prior Art
Wi-Fi technology, compliant with the IEEE 802.11abg standards and operating in the 2.4 to 2.5 GHz and 4.9 to 5.9 GHz bands, is today the best-placed technology for high-speed wireless transmissions in a domestic setting. The emerging standard 802.11n, derived from these standards, will enable a significant increase in speed and coverage in a domestic setting in the same frequency bands. In particular, the transmission of several video streams (HD and/or SD) between for example a set top box (STB) and several terminals (PC, TVs, etc.) or a high-speed data transmission, for example for an Internet connection, will be possible. MIMO (Multiple Input Multiple Output) techniques are then implemented with several synchronous RF transmit and receive channels. The single-band MIMO transmission circuit, called a “2T*3R” circuit (two transmit paths and three receive paths), is today often retained by suppliers of user terminals to provide the interface between the circuits of the front end module (FEM) linked to the antennas and the baseband digital circuits since this approach provides a good cost/performance compromise
In order to provide one or more video links with a good quality of service and a high-speed data link at the same time, the simultaneous use of 2.4 GHz and 5 GHz frequency bands can be considered. The most rational use is a video transmission in the 5 GHz band and a data transmission in the 2.4 GHz band since the latter is narrower and more congested. To meet these new demands, the terminal solutions conventionally adopted consist of front end modules (FEMs) linked to separate antennas and interfaced through RF circuits, i.e. RFICs (radio frequency integrated circuits), to baseband digital circuits operating in the corresponding frequency bands. The “2T*3R” MIMO techniques are often implemented for video transmission with an antenna diversity of order 3 for reception. An antenna diversity of order 2 can also advantageously be implemented in the 2.4 GHz band to improve the performance of the system.
The terminal 5G according to
The single-band MIMO transmission circuit M1 converts the RX1, RX2 and RX3 signals received simultaneously by the three antennas into a signal transmitted to the baseband digital processing circuit BB 5G, thereby performing a receive operation with a diversity of order 3. It also converts the signals transmitted by the circuit BB 5G into signals to be transmitted, TX1, TX2, by the antennas 1 and 2, thereby performing a transmit operation with a diversity of order 2.
In parallel, the terminal 2.4G, linked to the antennas 4 and 5 for receiving and transmitting data in the 2.4 GHz band includes a front end module FEM 2.4G linked to a circuit RFIC 2.4G and to respective baseband digital processing circuits BB 2.4G for receiving or transmitting signals with a diversity of order 2. The front end module FEM 2.4G includes a DPDT (Dual Pole Dual Throw) switch D1 which converts the signals transmitted or received by the antennas 4 and 5 into a receive or transmit signal on the points TX or RX of the MIMO transmission circuit M2 of the circuit RFIC 2.4G.
With this conventional approach, a group of five separate antennas is required, which results in major problems of size and cost.
The invention aims to overcome these drawbacks.
The invention consists of a terminal in a communication system linked to a group of antennas, the terminal being made up of a front end module connected to digital processing circuits via a circuit designed for MIMO techniques, for a simultaneous dual-band reception or transmission of video signals and data in a domestic environment.
At least two antennas (7, 8) linked to the terminal are broadband and dual-access, each of the accesses corresponding to a path for receiving or transmitting signals in a first or a second frequency band.
The front end module FEM comprises first switches (S1, S2) connected to the paths (A, B, C) for receiving or transmitting signals in the first frequency band, and second switches (D1) connected to the paths (D, E) for receiving or transmitting signals in the second frequency band.
The front end module FEM also comprises selective high-pass filters in the paths for receiving or transmitting signals in the highest frequency band.
This terminal therefore includes a smaller number of components and the number of antennas is also reduced.
In another embodiment, the front end module FEM comprises selective low-pass filters in the receive paths of the lowest frequency band.
Preferably, in the 802.11abg standard and the 802.11n standard, the first upper frequency band and the second lower frequency band correspond to the 5 GHz and 2.4 GHz bands respectively.
The invention is also a method for selecting different frequency bands in order to simultaneously transmit or receive video signals and high-speed data in a communication system with a plurality of synchronous transmit and receive channels, which system includes a group of antennas linked to respective baseband digital processing circuits BB via an FEM terminal and an RF circuit.
The video signals and the high-speed data are transmitted or received simultaneously in two different frequency bands, a first upper frequency band and a second lower frequency band, through dual-access dual-band antennas that are isolated from one another, before being transmitted, for the signals transmitted or received in the first frequency band, to switches of the RF circuit in this frequency band and the video signals and the data, received or transmitted in the upper frequency band on one of the accesses of the dual-band antennas, are filtered by high-pass filters (F1, F2, F3) for the upper-frequency-band reception before being switched on to the various transmit ports (TX1, TX2) or receive ports (RX1, RX2, RX3) of a first MIMO RF transmission circuit (M1) while the video signals and the data, received or transmitted in the lower frequency band on the other of the accesses of the dual-band antennas, are switched on to the various transmit ports (TX) or receive ports (RX) of a second MIMO RF transmission circuit (M2).
Preferably, the video signals and the data, received or transmitted in the lower frequency band on the other of the accesses of the dual-band antennas, are filtered by low-pass filters (F4, F5) for the lower frequency band.
The features and advantages of the invention mentioned above, and others, will become clearer on reading the following description given with reference to the accompanying drawings in which:
Since the circuit according to the prior art has been briefly described earlier, it will not be described again hereafter. Furthermore, the same references are used for the same items in the prior art circuit and in the circuits according to the invention.
The device, according to the invention, represented by
Implementing such a concept requires some precautions to be taken due to the simultaneous operation of the 2.4 GHz and 5 GHz circuitry, since there is a risk of the paths D and E, operating with the 2.4 GHz signals, becoming polluted by the 5 GHz signals and vice versa. To significantly improve the performance of the user terminal, a particular RF architecture is chosen, as follows. The three antennas are arranged to maximize the isolation between paths, and this can only improve the performance of the system operating in MIMO mode (independent antennas). For example, the dual-band antennas can be positioned at two ends, while the single-band antenna is located at the centre of the antenna structure.
The 5 GHz accesses of the antennas 7 and 8, for the transmission and reception of signals in the 5 GHz band, are connected via the path B and the switch S2, or via the path C, filters F and amplifiers a to the MIMO M1 operating at 5 GHz, while the other 2.4 GHz accesses of these antennas 7 and 8, for the transmission and reception of signals in the 2.4 GHz band, are connected via the paths D and E and switch D1, filters F and amplifiers a to the MIMO M2 operating at 2.4 GHz. The two MIMO circuits are independent and can operate in parallel.
In order to reduce mutual pollution between paths, a high-pass filter F1 is implemented in the path B to prevent the 2.4 GHz transmission interfering with the 5 GHz reception. In the path C, a high-pass filter F2 is also implemented in order that the 2.4 GHz transmission does not deteriorate the 5 GHz reception. In the path A, a high-pass filter F3 can also be implemented to prevent the 5 GHz reception from being degraded by the 2.4 GHz transmission.
In the paths D and E, a low-pass filter F4, F5 is implemented to prevent the 2.4 GHz reception from being degraded by the 5 GHz transmission. If the isolation between physically distant antennas is sufficient, the filters at A and E are unnecessary. It is clear that isolation between antennas, i.e. the layout, is important. A different polarization, for example, can lead to simplifying the FEM.
The observations that can be made concerning the implementing and dimensioning of the filters F1 to F5 are indicated by way of example in the following conditions:
With a dual-access antenna isolation: 18 dB
Antenna gain: 0 dBi
Power Pout delivered to the 2.4 GHz antennas: 18 dBm
Power Pout delivered to the 5 GHz antennas: 16 dBm
Reduced noise factor at 2.4 GHz LNA input: 6 dB
Reduced noise factor at 5 GHz LNA input: 6 dB
LNA input noise floor: −168 dBm/Hz
Isolation between close antennas: 20 dB
Isolation between antennas that are the furthest apart: 30 dB
Signal bandwidth: 20 MHz
Transmission C/N signal to noise ratio: 40 dB
Reception C/N signal to noise ratio required: 20 dB
Low-pass filter rejection at 2.4 GHz: 40 dB
Low-pass filter rejection at 5 GHz: 40 dB
As regards the risk of the 5 GHz reception signals on the path A becoming polluted by the 2.4 GHz signals for a power level of the interfering signal of −42 dBm (Pin=−42 dBm), while taking into account the bandpass filtering by the filter F on the receive path of 40 dB and an isolation between physically distant antennas of 20 dB, and with a noise level corresponding to Pin noise=−82 dBm, it is to be noted that the addition of a conventional 30 dB low-pass filter F3 results in an improvement in density from −155 dBm/Hz to −185 dBm/Hz. This filter is optional if the isolation between physically distant antennas is sufficient.
As regards the risk of the 5 GHz reception signals on the path B becoming polluted by the 2.4 GHz signals for a power level of the interfering signal of −40 dBm (Pin=−40 dBm), while taking into account the bandpass filtering by the filter F on the receive path and an isolation between physically distant antennas of 30 dB, and with a noise level corresponding to Pin noise=−70 dBm, it is to be noted that the addition of an additional 40 dB high-pass filter F1 is necessary. The values then become:
Pin signal=−70 dBm; Pin noise=−110 dBm; Density=−183 dBm/Hz.
As regards the risk of the 5 GHz reception on the path C becoming contaminated by the 2.4 GHz signals for a power level of the interfering signal of 0 dBm (Pin=0 dBm), while taking into account the bandpass filtering by the filter F on the receive path and an isolation between physically distant antennas of 30 dB, and with a noise level corresponding to Pin noise=−40 dBm, it is to be noted that the addition of an additional 70 dB high-pass filter F2 is necessary. The values then become:
Pin signal=−70 dBm; Pin noise=−110 dBm/Hz; Density=−183 dBm/Hz.
As regards the risk of the 2.4 GHz reception on the paths D and E becoming contaminated by the 5 GHz signals for a power level of the interfering signal of 44 dBm (Pin=44 dBm), while taking into account the bandpass filtering by the filter F on the receive path and an isolation between physically distant antennas of 30 dB, and with a noise level corresponding to Pin noise=44 dBm, it is to be noted that the addition of additional 30 dB low-pass filters F4 and F5 is necessary.
The density values then become:
Density=−187 dBm/Hz.
These filters are optional if the isolation between physically distant antennas is sufficient.
The invention is not limited to the embodiments described and a person skilled in the art will recognize the existence of various embodiments of the invention. Indeed, if the antenna proximity constraints are different, isolation between the antennas will be important and the values of the high-pass and low-pass filters will be dependent on it.
Different MIMO transmission circuits with receive and transmit diversity can be employed.
It is thus possible to envisage a higher-order diversity for reception in the 2.4 GHz frequency band. In that case, three antennas must be dual-access dual-band antennas and the front end module is adapted to switch signals to the different MIMO transmission modules.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0752808 | Feb 2007 | EP | regional |
