Telecommunications – Receiver or analog modulated signal frequency converter – Frequency modifying or conversion
Reexamination Certificate
2002-07-23
2004-11-23
Kincaid, Lester G. (Department: 2686)
Telecommunications
Receiver or analog modulated signal frequency converter
Frequency modifying or conversion
C455S333000, C455S323000
Reexamination Certificate
active
06823181
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a universal platform suitable for software defined radio and capable of handling multiple radio standards.
BACKGROUND INVENTION
After the first technical paper was presented in 1992, software defined radio (SDR) has been receiving much attention among researchers working on wireless communications (refer to J. Mitola III, D. Chester, S. Haruyama, T. Turletti, and W. Tuttlebee, “Globaliazation of Software Radio,” IEEE Communications Magazine, vol.37, no.2, pp.82-83, February 1999, and R. Kohno, “Prespective of Software Radio: Spatial and Temporal Communication Theory Using Adaptive Array Antenna for Mobile Radio Communications”, Proceeings on Microwave Workshops and Exhibition (MWE '97), December 1997). There is a conceptual reason and a technical reason behind this popularity (refer to J. Mitola III, “Technical Challenges in the Globalization of Software Radio,” IEEE Communications Magazine, vol.37, no.2, pp.84-89, February 1999).
The conceptual reason is that various wireless standards have been established through generations of wireless communication systems. Even in the same generation, several standards have been created in different regions.
As an example, the standardization efforts surrounding IMT2000/UMTS have tried to resolve the dispute over what the third generation standard should entail. Despite all of this, it still seems as if three slightly varying code division multiple access (CDMA) standards will be introduced in the near future.
For wireless local area networks (LAN), not only IEEE standards, but also de facto standards such as Bluetooth have gained wide acceptance among companies all over the world. Thus, a multiband multimode radio system is required to create a comfortable mobile computing environment. The reconfigurability of SDR is the answer to this problem.
The technical reason behind the popularity of the SDR concept is the development of reconfigurable devices for signal processing such as digital signal processors (DSP) and field programmable gate arrays (FPGA). The latest DSP's operate at speeds up to 1.1 GHz and offer performance of nearly 9 billion instructions per second. FPGA's can now provide densities of up to 2 million gates with low power consumption. These numbers are ever improving (refer to M. Cummings and S. Haruyama, “FPGA in the Software Radio,” IEEE Communications Magazine, vol.37, no.2, pp.108-112, February 1999, and F. J. Harris, “Configurable Logic for Digital Communications: Some Signal Processing Perspective”, IEEE Communications Magazine, vol.37, no.8, pp.107-111, August 1999).
Therefore, the real challenges facing SDR are the RF front-end, which is able to use the reconfigurability of the signal processing devices mentioned above and providing multimode and multiband communications.
In order to realize a multimode multiband SDR, the RF front-end should be able to support a wide range of frequencies and bandwidths. This task may be difficult with conventional RF front-end architectures (H. Tsurumi and Y. Suzuki, “Broadband RF Stage Architecture for Software-Defined Radio in Handheld Terminal Applications,” IEEE Communications Magazine, vol.37, no.2, pp.90-95, February 1999).
FIG. 1
is a block diagram of a conventional heterodyne receiver.
The heterodyne receiver
10
of
FIG. 1
comprises a receiving antenna
11
, a low noise amplifier (LNA)
12
, a radio-frequency (RF) filter
13
, an RF mixer
14
, an RP use local oscillator
15
, a first intermediate-frequency (IF) filter
16
, an IF mixer
17
, an IF use local oscillator
18
, a second IF filter, an automatic gain controlled (AGC) amplifier
20
, and an analog-to-digital converter (ADC)
21
.
This architecture requires frequency-dependent passive components such as a dielectric filter
13
in the RF stage and surface acoustic wave (SAW) filter
16
in the first IF stage. A ceramic or crystal filter
19
is also needed in the second IF stage. The center frequencies and bandwidth of these filters
13
,
14
, and
19
are not flexible and not wide enough to support a multiband radio receiver.
Though switched capacitor filter banks and precision direct synthesis may be a choice to achieve wider bandwidths and programmability, they are not applicable to mobile terminals due to their size and weight.
Thus, the candidate for the RF front-end for SDR is the direct conversion (DC) principle.
FIG. 2
is a block diagram of a conventional direct conversion receiver.
The direct conversion receiver
30
of
FIG. 2
comprises a receiving antenna
31
, an LNA
32
, RF mixers
33
and
34
, an RP use local oscillator
35
, a n/2 phase shifter
36
, low-pass filters (LPF's)
37
and
38
, AGC amplifiers
39
and
40
, and ADC's
41
and
42
.
In the direct conversion receiver
30
of
FIG. 2
, the received signal is down-converted directly to baseband by the quadrature mixer. The down-converted in-phase and quadrature (IQ) signals are prefiltered by the anti-aliasing LPF's
37
and
38
with variable cutoff frequency. They are converted to digital signals by IQ ADC's
41
and
42
and fed to the digital stage. The desired signal is selected by the software defined filter with programmable cutoff frequency.
The DC technique inherently has no image response, and the fixed-frequency image rejection filters can be eliminated. Furthermore, the anti-alias LPF can be designed with active, variable-bandwidth filters such as a switched capacitor embedded in an LSI chip.
In the conventional DC technique, the mixer has been used, however, in general it is difficult to design the mixer for a wide bandwidth. Therefore, if the conventional DC technique is applied to the software wireless system, improvement is necessary in point of widening the bandwidth.
Further, in the conventional direct conversion receiver, a sufficiently high local power is necessary in order to make the mixer operate with satisfactory characteristics. This invites an increases of power consumption of the receiver. Especially, when the carrier frequency is high, it is difficult to obtain a lower power consumption and a high local output power.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a universal platform for software defined radio capable of solving the DC offset problem and supporting very wide bandwidths.
According to the first aspect of the present invention, there is provided a universal platform for software defined radio, comprising an n (n being an integer of 3 or more)-port receiver including: a first input terminal receiving as input a received signal, a second input terminal receiving as input a local signal, a generating means for generating two signals having a phase difference based on at least one signal between the received signal input from the first input terminal or the local signal input from the second input terminal and including at least one output terminal for outputting the generated signal, and at least one power detector for receiving as input the output signal from the output terminal and detecting the signal level of the input signal; and a converter for converting the output signal of the power detector to a plurality of signal components included in the received signal or the local signal.
According to a second aspect of the present invention, there is provided a universal platform for software defined radio, comprising an n (n being an integer of 3 or more)-port receiver including a first input terminal receiving as input a received signal, a second input terminal receiving as input a local signal, a generating means for generating two signals having a phase difference based on at least one signal between the received signal input from the first input terminal or the local signal input from the second input terminal and including at least one output terminal for outputting the generated signal, and at least one power detector for receiving as input the output signal from the output terminal and detecting the signal level of the input signal; at least one analog-to-digital (A/D) conver
Abe Masayoshi
Amir-Alikhani Hamid
Brankovic Veselin
Haruyama Shinichiro
Kohno Ryuji
Frommer William S.
Frommer & Lawrence & Haug LLP
Kincaid Lester G.
Lee Sam S.
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