Showing papers on "Frequency-division multiplexing published in 1968"

Phased-array beam steering by multiplex sampling

Abstract: One approach to phased-array antenna beam forming and steering is to multiplex the element signals into a single channel. Appropriate "sampling" of the resulting multiplexed signal can provide electronically steered and shaped beams. This paper describes four practical system concepts for linear and ring arrays based on this approach and discusses significant interrelationships between the various concepts. For linear arrays of elements, the two alternatives are to frequency or time multiplex the element signals. Frequency multiplexing of the element signals produces time-multiplexed beam output signals, and time multiplexing the element signals produces frequency-multiplexed beam output signals. It is also shown here that appropriate correlation "sampling" may be used with either of these to produce easily one or more continuously and electronically steered signal bandwidth beam outputs. Ring arrays of elements may be multiplexed and "sampled" in a somewhat analogous pair of techniques. It is also pointed out that the beam steering in this case may be visualized as the linear phase steering of a set of linear phase modes into which the signal received at the array may be resolved. Ring array beam forming and steering may thus be directly understood in terms of the previous linear array techniques.

Resonant Transfer Between Filters of Uequal Bandwidth and Its Applications

Abstract: The resonant transfer process is extended to include greater generality. This leads to certain new applications. Baseband-to-baseband resonant transfer transmission has been used for a number of years in the area of time division switching. In addition, recently the more general concept of single-sideband-tosingle-sideband transmission, which would include the baseband-tobaseband case, has been used to obtain frequency division multiplexing. This technique allows time division switching and frequency division multiplexing to be combined into one common operation. Such an integrated system has been labeled integrated switching and multiplexing (ISAM). In this paper, the generality is carried one step further. The restriction that the input and output resonant transfer filters each cover a single-sideband frequency region has been removed. Instead, the filters are allowed to cover one or more such regions. This leads to the concept of lossless resonant transfer transmission between filters of unequal bandwidth. The reason for considering this is that several applications involving this type of operation have become apparent. Two of the more important of these applications have to do with the insertion of signaling information into the ISAM system and with establishing conferencing connections within the system. This new mode of resonant transfer transmission is rigorously analyzed and the applications discussed. These techniques are equally applicable to conventional basebandto-baseband time division switching.

Signal insertion and conferencing in a resonant transfer integrated time division switching and frequency division multiplexing communication system

Abstract: 1,207,252. Automatic exchange systems. INTERNATIONAL BUSINESS MACHINES CORP. 5 June, 1968 [15 Sept., 1967], No. 26679/68. Heading H4K. In a t.d.m. switching system employing resonant transfer filters in each line, a source of signals is available to anyone or any number of the lines simultaneously by way of a wideband filter. If the number of time slots in a multiplex cycle is X, the bandwidth of the wide band filter over which signals are drawn is X times the bandwidth fs/2 of the resonant transfer line filters, fs being the sampling frequency. The signals may be supervisory tones or may be the output of conference circuits as shown in Fig. 3. A conference circuit such as 330, comprises a wideband filter 305 accepting as many sidebands as there are time slots in the multiplex, a low pass filter 309 passing only the base band, an amplifier A, and a wideband filter 315. Wideband filter 305 is gated to highway 277 in the time slots of incoming lines and channels to the conference, while wideband filter 315 is gated to the highway in the time slots of the outgoing lines and channels to the conference. The system has incoming and outgoing local lines served by lowpass resonant transfer filters, and has incoming and outgoing frequency division multiplex lines the channels of which are served by bandpass filters giving resonant transfer over the highway, this system being described in Specification 1,057,259.