BACKGROUND OF THE INVENTION
Present telecommunication system technology includes a wide variety of wireless networking systems associated with both voice and data communications. An overview of several of these wireless networking systems is presented by Amitava Dutta-Roy, Communications Networks for Homes, IEEE Spectrum, pg. 26, December 1999. Therein, Dutta-Roy discusses several communication protocols in the 2.4 GHz band, including IEEE 802.11 direct-sequence spread spectrum (DSSS) and frequency-hopping (FHSS) protocols. A disadvantage of these protocols is the high overhead associated with their implementation. A less complex wireless protocol known as Shared Wireless Access Protocol (SWAP) also operates in the 2.4 GHz band. This protocol has been developed by the HomeRF Working Group and is supported by North American communications companies. The SWAP protocol uses frequency-hopping spread spectrum technology to produce a data rate of 1 Mb/sec. Another less complex protocol is named Bluetooth after a 10th century Scandinavian king who united several Danish kingdoms. This protocol also operates in the 2.4 GHz band and advantageously offers short-range wireless communication between Bluetooth devices without the need for a central network.
The Bluetooth protocol provides a 1 Mb/sec data rate with low energy consumption for battery powered devices operating in the 2.4 GHz ISM (industrial, scientific, medical) band. The current Bluetooth protocol provides a 10-meter range and a maximum asymmetric data transfer rate of 723 kb/sec. The protocol supports a maximum of three voice channels for synchronous, CVSD-encoded transmission at 64 kb/sec. The Bluetooth protocol treats all radios as peer units except for a unique 48-bit address. At the start of any connection, the initiating unit is a temporary master. This temporary assignment, however, may change after initial communications are established. Each master may have active connections of up to seven slaves. Such a connection between a master and one or more slaves forms a “piconet.” Link management allows communication between piconets, thereby forming “scattemets.” Typical Bluetooth master devices include cordless phone base stations, local area network (LAN) access points, laptop computers, or bridges to other networks. Bluetooth slave devices may include cordless handsets, cell phones, headsets, personal digital assistants, digital cameras, or computer peripherals such as printers, scanners, fax machines and other devices.
The Bluetooth protocol uses time-division duplex (TDD) to support bi-directional communication. Frequency hopping permits operation in noisy environments and permits multiple piconets to exist in close proximity. The frequency hopping scheme permits up to 1600 hops per second over 79 1-MHZ channels or the entire 2.4 GHz ISM spectrum. Various error correcting schemes permit data packet protection by ⅓ and ⅔ rate forward error correction. Further, Bluetooth uses retransmission of packets for guaranteed reliability. These schemes help correct data errors, but at the expense of throughput.
The Bluetooth protocol is specified in detail in Specification of the Bluetooth System, Version 1.0A, Jul. 26, 1999, which is incorporated herein by reference.
In wireless communication systems such as described above, the well-known disadvantageous phenomenon of fading is encountered. Conventional transmit diversity techniques can provide several dB's of gain to thereby at least partially overcome the fading problem. Some known transmit diversity schemes require an estimate of the channel at the transmitter, which estimate can be made from previous receptions at the same frequency. However, because the operating environment is not totally static, such estimates are sometimes not very accurate.
Another known technique for overcoming fading is antenna space time transmit diversity. An example of this technique is disclosed in U.S. Ser. No. 09/205,029 (Attorney Docket No. TI-28441), filed on Dec. 3, 1998 and incorporated herein by reference. The space time transmit diversity disclosed therein is bit level space time transmit diversity for use with linear modulation schemes such as QPSK modulation. However, bit level space time transmit diversity cannot be used in wireless communication systems that utilize non-linear modulation schemes, for example the GFSK modulation scheme utilized in Bluetooth systems.
It is therefore desirable to apply space time transmit diversity techniques in wireless communication systems that utilize nonlinear modulation.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention applies space time transmit diversity to achieve diversity gains in wireless communication systems that utilize nonlinear modulation schemes. In particular, space time transmit diversity (STTD) is applied at the block level to an original block of bits advantageously to reduce the effects of fading in wireless communication systems that use nonlinear modulation schemes. At the receiving end, fading parameters are estimated and the properties of complex conjugates are utilized to produce a result that is representative of the original block of bits.
FIG. 1 diagrammatically illustrates pertinent portions of exemplary embodiments of a transmitting station that implements block level space time transmit diversity according to the invention.
FIGS. 2-4 diagrammatically illustrate pertinent portions of exemplary embodiments of a receiving station which implements block level space time transmit diversity according to the invention.
FIG. 5 diagrammatically illustrates pertinent portions of further exemplary embodiments of a transmitting station according to the invention.
FIG. 6 illustrates exemplary operations which can be performed by the receiving station of FIGS. 2-4.
FIG. 7 illustrates exemplary operations which can be performed by the transmitting station of FIG. 1.
FIG. 8 illustrates exemplary operations which can be performed by the transmitting station of FIG. 5.
FIG. 9 illustrates the communication performance of a nonlinear modulation wireless communication system with (and without) block level space time transmit diversity according to the invention.
FIG. 1 diagrammatically illustrates pertinent portions of exemplary embodiments of a transmitting station according to the invention. For example, the transmitting station of FIG. 1 could be a Bluetooth master or slave device. In FIG. 1, input digital information bits are applied to a block formatter 11 which establishes from the input bits an original block of bits having two parts x1 and x2, shown generally at 12. Parts x1 and x2 each include a plurality of bits. The two-part block of bits 12 is input to a nonlinear modulator such as an FSK (or GFSK) modulator 13 which uses conventional techniques to modulate a carrier signal with the block of bits to produce at 14 a modulated block of information including a first part a and a second part b which respectively correspond to the parts x1 and X2 at 12.
The two-part modulated block at 14 is input to an STTD encoder 15 which outputs at 9 a re-ordered two part block including a first part −b* which represents the negative of the complex conjugate of the second part b of the modulated block at 14, and also including a second part a* which is the complex conjugate of the first part a of the modulated block at 14. Complex conjugation as described herein can be performed in any desired conventional manner. For example, if m= cos (wcτ−φ(t)), then the complex conjugate m*= cos (wcτ−φ(t)). As another example, the part a* of FIG. 1 can be produced by using the negative of the bits that were used to produce the modulated part a in FIG. 1, that is, by also modulating −x1 at 13. In such embodiments, the modulator 13 can provide both a* and b*, as shown by broken line in FIG. 1 (i.e., the modulator 13 performs the complex conjugate function of the encoder 15), so the encoder at 15 need only perform the re-ordering and negation operations.
The block output at 9 from the STTD encoder 15 is applied to a transmit processing section 17, and the modulated block 14 output from the modulator 13 is applied to another transmit processing section 19. The transmit processing sections 17 and 19 utilize conventional transmit processing techniques to effect transmission of the blocks 9 and 14 across a wireless communication link 18 (e.g., a Bluetooth link) via respective antennas 10 and 16. In the example of FIG. 1, transmission of the part a * of block 9 corresponds in time with transmission of the part b of block 14, and transmission of the part −b* of block 9 corresponds in time with transmission of the part a of block 14, thereby providing space and time transmit diversity. Also as shown in FIG. 1, the wireless communication channel associated with antenna 10 has a fading parameter designated as α1, and the wireless communication channel associated with antenna 16 has a fading parameter designated as α2.
FIGS. 2 and 3
diagrammatically illustrate pertinent portions of exemplary embodiments of a receiving station according to the invention. For example, the receiving station could be a Bluetooth master device or a Bluetooth slave device. As shown in FIG. 2
, the wireless communication signals transmitted by antennas 10
of FIG. 1
are received at an antenna 20
of a wireless communication interface. The antenna 20
is coupled to a receive processing section 21
of the wireless communication interface, which utilizes conventional receive processing techniques to produce from the received antenna signals a block of information including a first part c and a second part d, as designated generally at 22
. The block at 22
is input to a separator 23
which separates the block into its constituent parts c and d. Recalling from FIG. 1
that blocks 9
were transmitted via the respective antennas 10
having the respective fading parameters α1
associated therewith, the parts c and d in FIG. 2
can be expressed as follows:
c=α 1 a−α 2 b *
Equation 1 d=α 1 b+α 2 a *
, Equation 2
- where the superscript “*” denotes the complex conjugate.
The receiving station can use conventional techniques to produce estimates αE1 and αE2 of the respective fading parameters αe1 and αe2. For example, a fading parameter estimater shown generally at 200 can be a conventional linear receiver, which provides fading parameter estimates in its normal operation. The fading parameter estimates αE1 and αE2 can be determined, for example, based on earlier transmissions received individually from the respective antennas 10 and 16, and can be stored in a suitable database (not explicitly shown). Using the estimated fading parameters, the following two signals can be formed:
r 1=αE1 * c+α E2 d * Equation 3
r 2=−αE2 c *+α* E1 d. Equation 4
In FIG. 2, the multiplier pairs at 24 and 26, the adders at 25 and 27, and the complex conjugators at 201, 202, 28 and 29 form a combiner that combines the parts c and d with the estimates αE1 and αE2 to produce the combined result signals r1 and r2 as defined by Equations 3 and 4 above. Combining Equations 3 and 4 with Equations 1 and 2, utilizing the symmetry of complex conjugates, and assuming that αE1≈α1, and αE2≈α2 the signals r1 and r2 can be expressed as follows:
r 1=(|αE1|2+|αE2|2)a Equation 5
r 2=(|αE1|2+|αE2|2)b Equation 6
As illustrated in FIG. 3, the signals r1 and r2 are input to a block formatter 31 which formats the signals r1 and r2 into a block of information at 32 having a first part r1 and a second part r2. This two-part block at 32 is input to a nonlinear (such as an FSK or GFSK) demodulator 33 which uses conventional demodulation techniques to produce at 34 the receiving station's determination of the original block of bits (see also 12 in FIG. 1).
FIG. 4 diagrammatically illustrates further exemplary embodiments of a receiving station according to the invention. In the embodiment of FIG. 4, the signals r1 and r2 from FIG. 2 are input to respective parallel nonlinear demodulators 41 which use conventional demodulation techniques to produce the receiving station's determination of the first and second parts x1 and X2 of the original block of bits (see also 12 in FIG. 1).
FIG. 5 diagrammatically illustrates pertinent portions of further exemplary embodiments of a transmitting station according to the invention, which can be used in conjunction with the receiving station of FIG. 4. In the embodiment of FIG. 5, the input bits are applied to a separator 51 which produces therefrom the first and second parts x1 and x2 (see 12 in FIG. 1) in parallel format, thus providing the original block of bits in parallel format. The parts x1 and x2 are applied to respective parallel nonlinear modulators 54, which utilize conventional modulation techniques to produce a modulated block in parallel format, including the parts a and b which respectively correspond to the parts x1 and x2 (see also FIG. 1). The parts a and b are input to a block formatter 55, which produces at 56 a block of information including the parts a and b, which block can then be input to the STTD encoder 15 and the transmit processing section 19 of FIG. 1. Thus, the embodiment of FIG. 5 provides an alternative arrangement for producing the two-part modulated block illustrated generally at 14 in FIG. 1.
FIG. 6 illustrates exemplary operations which can be performed by the receiving stations of FIGS. 2-4. After a block of information is received at 61, the block is divided (separated) into two parts at 62, and the signals r1 and r2 are formed at 63. Thereafter, the signals r1 and r2 are demodulated (and downscaled) at 64 to produce the receiving station's determination of the original block of bits.
FIG. 7 illustrates exemplary operations which can be performed by the transmitting station of FIG. 1. At 71, a two-part block of bits is established (see 12 in FIG. 1). At 72, the two-part block of bits is modulated to produce a two-part original modulated block (see 14 in FIG. 1). At 73, the two parts of the original modulated block are re-ordered and complex-conjugated, and at 74 one of the re-ordered, complex-conjugated parts is negated, thereby producing an STTD block (see also 9 in FIG. 1). At 75, the original modulated block and the STTD block are transmitted (in the timewise relationship described above) using respective first and second antennas.
FIG. 8 illustrates exemplary operations which can be performed by the transmitting station of FIG. 5. At 81, the input bits are separated into two parts (original block in parallel format). At 82, the two parts are respectively modulated to produce two corresponding modulated parts (modulated block in parallel format). At 83, the modulated parts are formatted into a two-part modulated block. From this point, operations can proceed to 73 in FIG. 7 (see broken line in FIG. 7) and, after the operations at 75 in FIG. 7, operations can return to 81 (see broken line in FIG. 7).
FIG. 9 illustrates exemplary simulation results for a conventional nonlinear-modulated wireless communication system at 92 and for a nonlinear-modulated wireless communication system which utilizes space time transmit diversity according to the invention at 94. The curve 94 demonstrates better performance.
It will be evident to workers in the art that the embodiments of FIGS. 1-8 can be readily implemented, for example, by suitably modifying software, hardware, or a combination of software and hardware, in conventional wireless transmitting and receiving stations that support plural transmit antennas, for example Bluetooth master and slave devices.
Although exemplary embodiments of the invention are described above in detail, this does not limit the scope of the invention, which can be practiced in a variety of embodiments.