PERHUTATION MODULATION FOR ADVANCED
`
`RADIO PAGING
`
`Dr. Rade Petrovic
`Center for Telecommunications
`University of Mississippi, University, as 38677
`
`Halt Roehr
`Telecommunication Networks Consulting
`11317 South shore Road, Reston, VA 22090
`
`Dennis Cameron
`MTEL Technologies
`P.O. Box 2469, Jackson, MS 39225
`
`ABSTRACT
`
`Themulticarrierpermutationmodulation
`technique proposed in this paper provides
`higher bit rates and spectrum efficiencies
`than that achieved in any state—of—the—art
`radio paging system. It can be used in
`simulcast
`networks with
`high
`power
`transmitters. where long symbol
`intervals
`and noncoherent detection are required. The
`technical
`feasibility of
`the
`proposed
`modulation technique is established through
`a set of laboratory and field experiments.
`Variations
`of
`the
`proposed modulation
`technique are discussed with regard to
`performance and complexity of receivers and
`transmitters.
`
`I.
`
`INTRODUCTION
`
`Current radio paging systems deliver
`numeric, alphanumeric. or tone only (beep)
`messages to small,
`low power. receive only
`devices known as pagers. Typically.
`the
`gross bit rate of 1200 bps
`is achieved
`through a 25 Khz radio channel by binary
`Frequency Shift Keying
`(FSK). Recently,
`MTEL, Jackson. as, has pioneered a step up
`of bit rate to 2400 bps. by a modification
`of its existing network. The next generation
`paging system, ERMRS (European Radio Message
`system), will achieve 6250 bps in 25 kHz
`channel by a 4—level FSK modulation.
`
`Since there is no return channel for
`acknowledgement
`and/or
`user
`location
`tracking (for possible hand—offs to nearest
`network transceiver). special care has to be
`taken to boost the reliability of reception
`and coverage area. A major contribution to
`these goals can be made by simulcasting,
`i.e. by the simultaneous broadcast of
`the
`same information,
`in the same channel, by a
`number of
`transmitters with overlapping
`coverage areas .
`
`The development of lap-top and palm-top
`PCs, which can conveniently deal with longer
`alphanumerical messages
`than
`standard
`pagers, has increased pressure for increased
`
`bit rates in paging radio channels. Also the
`spectral efficiency of
`the existing paging
`channels
`is
`increasingly
`questioned.
`especially
`in
`comparison with
`cellular
`networks.
`
`This paper describes our efforts to
`increase
`both
`bit
`rate
`and
`spectral
`efficiency in simulcast paging networks,
`while keeping receivers
`simple.
`and
`low
`power consumption devices.
`
`II PROPOSED MODULATION TECHNIQUE
`
`First we propose doubling the channel
`bandwidth
`in
`order
`to
`allow higher
`throughput. This should be done by moving
`the current emission mask boundaries away
`from the center frequency by +/— 12.5 kHz.
`This would give a 35 kHz pass band in the
`middle of
`the channel and 7.5 kHz guard
`bands on each side for the skirts of
`the
`spectrum.
`(See dashed lines in Figs.
`1 and
`2).
`
`In order to fully utilize the allocated
`spectrum, and provide fast fal1—off of
`the
`spectrum in the guard band we propose eight
`subcarriers spaced 5 kn: apart,
`so that
`there is exactly 35 kHz spacing between end
`subcarriers. Further we propose that during
`each symbol interval a combination of
`four
`distinct carriers is ON, while other
`four
`are OFF. This type of modulation falls into
`general class of permutation modulation,
`[1]
`which has features of constant energy for
`each symbol. efficient spectrum utilization
`and low requirement
`for
`symbol energy to
`noise
`density
`ratio
`[2].
`It
`can
`be
`classified also as a Hulticarrier Modulation
`[ICE]
`[3] with properties of good immunity
`to impulse noise and fast fades, and no need
`for equalization. The proposed code book has
`H distinct symbols, where
`8!
`(3-4) :4:
`
`= 70
`
`(1)
`
`- I,
`”' C‘
`
`are
`
`We propose that 64 out of 70 symbols
`used
`for data
`transmission, which
`
`0-7803-l257~0/93/$3.00 © 1993 IEEE.
`
`g
`
`Petitioners, Ex. 1013, Page 1
`
`Petitioners, Ex. 1013, Page 1
`
`

`
`corresponds to 6 bits per symbol, while the
`remaining
`6
`symbols
`are
`reserved
`for
`overhead
`funct ions
`(syn chroni zation ,
`control, etc). Symbols are transmitted at a
`4 kbaud rate, which gives a gross bit rate
`of 24 kbps.
`
`The spectrum efficiency of the proposed
`modulation is 0.48 bps/Hz, which is much
`higher
`than
`standard
`1200
`bps
`paging
`channels,
`(0.048 bps/Hz). or even ERMES
`system.
`(0.25 bpslnz). This is still not as
`good as
`some digital cellular networks,
`which can be attributed to the following
`differences.
`
`The spectrum mask for the paging system
`to be
`tighter
`in order
`to reduce
`has
`interference when a foreign transmitter in
`an adjacent
`channel
`is closer
`than the
`monitored transmitter (near-far problem). In
`cellular systems the network detects user
`proximity to different antenna sites and
`switches connection to the nearest
`one
`(handoff
`feature) .
`This
`effectively
`eliminates the near—far problem and allows
`a higher level of interchannel interference.
`
`environment
`simulcast
`the
`Further,
`prevents using coherent detection, since a
`moving pager would need to rapidly switch
`lock
`from one
`transmitter
`to
`another
`according
`to
`fading
`variations.
`This
`eliminates
`implementation of quadrature
`modulation techniques and effectively halves
`the efficiency.
`power
`DC
`receiver
`the
`Finally,
`efficiency dictates operation with brief
`receiver enable intervals (tens of symbols)
`followed by extended "sleep" periods, which
`prevents
`complex equalization algorithms
`based on equalizer
`training procedures.
`Therefore most of the modulation techniques
`currently used in cellular systems are not
`applicable in paging networks.
`
`I I I EXPERIMENTS
`
`technical
`the
`to investigate
`In order
`feasibility of
`the
`proposed modulation
`technique we have carried out
`a set of
`laboratory and field experiments at
`the
`University of Mississippi
`in the 930 MHz
`frequency
`band.
`The
`transmitters
`are
`constructed by Glenayre, Quincy,
`IL. Bach
`transmitter has four subtransmitters capable
`of I-PSK over a subset of the 8 frequencies.
`Outputs of the subtransmitters are combined
`and
`sent
`to
`a
`common
`antenna.
`Two
`transmitters were
`installed seven miles
`apart
`and
`synchronized
`to
`provide
`a
`simulcast overlap area with approximately 35
`dnuv/m signal strength.
`
`A receiver, constructed by Wireless Access,
`San Jose. CA, consists of an RF section
`which
`down
`converts
`the
`signal
`to
`a
`frequency band
`below 100
`kHz,
`an All)
`converter, a DSP processor which performs
`signal detection through DPT analysis. and
`a PC to control
`the operation and present
`results. Error
`free reception has
`been
`
`achieved both in laboratory and field tests
`for several hours, which corresponds to a
`BER < 10'’ .
`
`transmitter
`spectrum at
`signal
`The
`output is presented in Fig. 1, and 2. Fig. 1
`shows
`a
`spectrum of
`a
`single
`symbol
`(frequencies 1. 2. 4. and 8 ON, and 3, 5, 6,
`7 OFF)
`repeatedly transmitted. It shows a
`low level
`intermodulation products.
`The
`dashed line represents the proposed emission
`mask. with the pass—band level 6 dB above
`peaks, corresponding to the level obtained
`when all subtransmitters broadcast on the
`same frequency.
`
`Fig. 2 shows the spectrum of the signal
`sending pseudo random data (a repeated 512
`symbols
`long message),
`together with the
`emission mask (dashed line). It is evident
`that the allocated frequency band is fully
`utilized, which
`indicates
`the
`spectrum
`efficiency of
`the
`proposed modulation
`technique.
`
`the spectrum of several
`shows
`3
`Fig.
`isolated symbols the signal obtained by PFT
`processing in a digital oscilloscope. The
`FFT window was rectangular with 200 us width
`(which
`corresponds
`to
`a
`5
`kHz
`bin
`separation), synchronized externally to fit
`the middle of
`the 250 pa symbol
`interval.
`Four
`traces are shown in the plot,
`each
`obtained
`for different
`symbol.
`Such
`a
`diagram corresponds to eye diagrams, except
`it is in frequency domain instead of
`the
`time domain.
`It
`shows
`that
`symbols
`are
`distinguishable by a proper processing.
`
`IV POSSIBLE VARIATIONS
`
`considered
`that were
`Alternatives
`include multicarrier on-off keying (HOOK)
`with all eight
`subcarriers
`independently
`keyed. This would increase the bit rate to
`32 kbps, but increase the complexity of both
`transmitters and receivers.
`
`transmitters would require eight
`The
`subtransmitters with
`amplitude modulated
`power amplifiers, and one more step in the
`cascade
`of
`hybrid
`circuit
`combiners .
`Alternately a single linear power amplifier
`could be used, with symbols generated by DSP
`processing in the baseband, brought up to
`the
`target
`frequency
`range
`by
`SS3
`modulation. This approach is expected to
`have difficulties meeting the emission mask,
`due to intermodulation products.
`
`increase
`system would
`MOOK
`The
`complexity of the receiver with respect
`to
`automatic gain control and threshold setting
`for
`subcarrier
`detection.
`Alternative
`receiver design, with battery of filters
`instead of EFT processing, is rejected based
`on computer simulation which predicted high
`intercarrier interference.
`
`;
`
`Petitioners, Ex. 1013, Page 2
`
`Petitioners, Ex. 1013, Page 2
`
`

`
`10dB/
`
`§[50dB
`
`1
`
`i
`I
`
`, 1
`
`;
`
`---____1
`
`1
`
`.1:
`
`%rJM
`3
`«
`SPF: 1DO'r<H;z
`CPU‘: 930. QM!--iz
`Fig.
`1 Spectrum of a single symbol repeatediy transmitted
`
`i3_E§_3OOHz
`
`‘/B1'r<Hz
`
`20.0dBm
`RL:
`F“ “’I
`I
`
`1DdB/
`! ”"
`
`“i”
`
`fl[5DdB
`
`§j_3s
`
`‘ SPF:1DOkHz
`CNF:93G.9MHz A
`Fig.
`2 Spectrum of the signal carrying a pseudo random data
`
`aa3ooHz
`
`VB1kH2
`
`Peti_’;i9_r_1_<§§, Ex. 1013, Page 3 H
`
`Petitioners, Ex. 1013, Page 3
`
`

`
`22-Nov-92
`19:21:25
`
`:Mn(FFT(|))
`19 kHz
`
`1 2a nu
`
`DC 5
`
`21UDC{a
`
`F‘
`
`2nc17.av
`
`D STOPPED
`
`Fig.
`
`3 Frequency domain eye diagram obtained by EFT processing
`
`V
`
`CONCLUSION
`
`The permutation modulation technique
`delivers higher bit
`rates
`and better
`spectrum
`efficiency
`than
`modulation
`techniques currently used for paging. The
`higher efficiency attained in cellular
`networks
`is
`a
`result
`of
`the
`inherent
`differences in the type of services offered.
`The choice
`is made based on
`simulcast
`operation with long symbol
`intervals and
`noncoherent detection. and moderate cost,
`low power
`receiver
`based
`on digital
`processing.
`
`Laboratory and field tests proved the
`technical
`feasibility of
`the
`proposed
`technique.
`The
`research
`regarding
`optimization of receivers and transmitters,
`symbol
`synchronization based on digital
`processing, code table optimization, etc.,
`is underway.
`
`been
`This modulation technique has
`included in HTBL's petition to the FCC for
`the Nationwide Wireless Network service [4],
`and,
`the
`FCC has granted a
`tentative
`pioneers preference to this proposal [5].
`
`REFERENCES
`
`"Permutation modulation“,
`D. slepian,
`Proceeding of the IEEE, March 1965. PD.
`228-237.
`‘The Performance of PSK
`E. Brookner,
`Permutation Modulation
`in
`Fading
`Channels and Their Comparison Based on
`a General Method for the comparison of
`H-ary Hodu1ations',
`IEEE Trans.
`on
`Comm. Tech., Vol.
`cou—17, No. 6, Dec.
`1969. PD 616-639.
`'Mu1ticarrier
`J.A.C.
`Birnhan,
`Modulation for Data Transmission: An
`Idea Whose
`Time Has
`Come".
`IEEE
`Communications Magazine, May 1990. pp.
`5-14.
`Mobile Telecommunications Technologies
`Corporation. "Petition for Rulemaking
`to Allocate 150 kHz in the 930-931 MHz
`Band
`and
`to Establish Rules
`and
`Policies
`for
`a Nationwide Wireless
`Network (NWN) Service", Before the FCC,
`Nov. 12, 1991.
`Communication
`Personal
`FCC,
`"New
`Services Proposed (Gen. Docket No. 94-
`314, BT Docket 92-100)", FCC News, July
`17. 1992.
`
`;
`
`Petitioners, Ex. 1013, Page 4
`
`Petitioners, Ex. 1013, Page 4