Extras din curs
Chapter 1
MULTIPLE ACCESS TECHNIQUES
1.1. THE MAIN ACCESSING TECHNIQUES USED IN MOBILE
COMMUNICATIONS: PERFORMANCE AND CHARACTERISTICS
1.1.1. Duplex transmissions
Duplex transmission – communication between BS and MS
• The link between the base and the mobile station is called downlink in European
terminology and forward link in U.S. terminology;
• The link between the mobile station and the base station is called uplink in European
terminology and reverse link in U.S. terminology;
The duplex transmission can be achieved using frequency or time division.
• frequency division duplexing –
- FDD offers two frequency bands for each user. T
- each duplex channel consists of two simplex channels, each one is transmitted on
a different frequency carrier and in another frequency band.
- Both mobile and base stations have to be equipped with two antennas and a
duplex (made of radio frequency filters which protect the receiver from
interference with adjacent channels) which permits sending and receiving
messages simultaneously through both channels.
- frequency separation between the uplink and the down link channels, is a
constant value of the system and doesn’t depend on the type of channel.
• time division duplexing –
- TDD uses different temporal slots for the uplink and the down link.
- If the difference between the two allocated slots is relatively small, the
transmission and reception of data appears to be simultaneous to the user.
Fig. 1.1. The description of FDD (a) si TDD (b) techniques
1.1.2. Multiple access in mobile communications
Three fundamental techniques that are usually used:
• frequency division multiple access – FDMA;
• time division multiple access – TDMA;
• code division multiple access – CDMA.
Mobile communication systems can have large or narrow bandwidth, depending on the
ratio between the band space occupied by a single user and the coherence band of the
transmission channel (which represent the frequency range where the amplitude of two
cosine-function components, on different frequencies are related with one another).
(A) The systems of communications with narrow bandwidth are those systems where the
band used by a channel (user) is smaller or approximately equal to the coherence bandwidth
of the communication channel. In this case the radio frequency spectrum is divided in a
number of narrow bandwidth channels as large as possible, each user being allowed to use
such a channel. The multiple access technique can be FDMA or TDMA.
• In narrowband FDMA systems, each user has allocated a carrier frequency and a
frequency band which he uses individually the whole time of the transmission. The
duplex communication is achieved by frequency division (FDD). The principle FDMA
/ FDD is illustrated in figure 1.2.
Preview document
Conținut arhivă zip
- 0_BPSK_QPSK_done.pdf
- 1_Prez_Mult_Access_07.pdf
- 2_Spread Spectrum_07.pdf
- 2_UWB_07.pdf
- 3_IS95_07A.pdf
- 4_Walsh_07.pdf
- 5_PNseq_07.pdf
Alții au mai descărcat și
Comutarea tranzistorului bipolar Scopul lucrarii Scopul lucrarii: se studiaza regimul de comutare al tranzistorului bipolar, se masoara timpii de...
1. Caracteristici 80C51 este un microcontroler vechi dar foarte raspîndit. Este necesara cunoasterea sa întrucît el a pus bazele unei familii de...
Amplificatorul operational introducere Termenul amplificator operational, introdus în 1940 se refera la un tip special de amplificator care,...
CAPITOLUL 1 Elemente de algebra booleeana Algebra Boole a fost conceputa de catre matematicianul englez George Boole (1815 ¸ 1864) ca o metoda...
I.Structura unui microcalculator.Definitii …:::1.1 Componentele multifunctionale ala unui microcalculator:::… Microcalculatorul, structurat ca o...
Te-ar putea interesa și
I. Conditii impuse 1. Termometru digital cu 3 digiti care masoara 4 temperaturi 2. Gama de masura: -40˚ C÷100˚C 3. Eroarea de masura: ±0.5˚C (...
1. Introduction I. BPSK modulation/demodulation Sending a BPSK signal means to transmit binary data, noted d(t), (periodic by Tb) modulating...