One Space P a r k .Redondo Beach, California SUMMARY The translation from time division multiplexed data f o r m a t s to frequency division multiplexed data formats is considered. menting the translation a r e presented. sent three types of digital single-sideband modulation. I t i s shown that the design of the three translators can be reduced to a computationally-efficient form of a multirate digital filter. Seven f o r m s of implementing the multirate digital filter a r e developed. The parall e l f o r m s a r e shown to be the l e a s t sensitive to coefficient e r r o r s . However, it i s noted that the direct f o r m s a r e not so sensitive a s to be impractical to i mplement. This i s singificant because single-rate, direct form f i l t e r s with narrow passbands and s h a r p transition regions a r e usually much too sensitive to coefficient e r r o r s to be considered practical. Basic results that a r e used i n the analysis and design of the multirate digital filters a r e derived. A 12-channel TDM-FDM translator design example i s presented. This example introduces a simulation and analysis program (SANDS) which i s used to evaluate the TDM-FDM translator performance.Three methods of efficiently impleThese r e p r e -
1, INTRODUCTIONTwo methods of combining many information channels for efficient transmission a r e i n wide use today: time division multiplexin TDM) and frequency division multiplexing (FDM).fl() FDM h a s been used by the telephone companies for many y e a r s . Improvem e n t s i n digital technology i s increasing the use of TDM. tion for many y e a r s and a means of translatingbetween them i s needed. tation of digital TDM-to-FDM translators.It appears that both methods will be i n operaThis paper examines the implemenSection 2 p r e s e n t s a unified approach to the prob-The problem based on the implementation of three types of digital SSB (single-sideband) modulators. lem i s reduced to designing a special type of multirate digital filter. filter and presents guidelines f o r i t s implementation. The hardware requirements for the three types of SSB modulators a r e compared. of a i2-channel TDM-FDM translator.Section 3 discusses the design of the Section 4 gives an example
DIGITAL TDM TO FDM TRANSLATORSA digital TDM to FDM translator i s i n a functional sense a digital SSB modulator. separated into N channels which a r e then SSB modulated to N different frequency slots to form an FDM signal. To provide economic competition to analog techniques, the digital SSB modulators m u s t be highly efficient in their use of digital hardware. Three types of digital SSB modulators a r e presented. These a r e derived from the three methods of generating SSB signals that employ linear time-invariant filters:(2) the Weaver modulator, (4) the Hartley (phase splitting) modulator, ( 7 ) and the bandpass filter type SSB modulator. The TDM input i s The mathematical formulation of the SSB signal i s CH1315-1/78/0000-0184$00.75 ( c ) 1978 IEEE Electrical Engineering Dept. W. Lafayette, In...