angielski > polski Technika/inżynieria Telekomunikacja Metody dostępu do bezprzewodowych systemów komunikacji

"poziom dźwięku" czy "poziom szumu" w tym kontekście?

Kontekst

The initial ranging transmission may be used by any SS that wants to synchronize to the system channel for
the first time. In one embodiment of the invention, a control message from the BS may specify the sub-bands that an initial ranging signal can use. All sub-bands or, for example, a specified number of the sub-bands starting from the lowest frequency offset may be allowed for initial ranging. Maximally, only Nsh = a Nsp / LCpeÌ shifts are preferred for interferencefree code separation among different shifts of a ranging signal where axÌ denotes the flooring function (i.e., the maximum integer that is not greater than x), LCPe is the length of an extended CP and Nsp is the FFT size of the special FFT symbol (209 of FIG 2) that may be multiples of the regular FFT size N. If some interference between estimated channels can be tolerated, that maximal number may be even increased. In general, more shifts can be used at the expense of increased interference. But a good practice is setting the number of shifts to Nsh’=aNsp/ LCPeÌ so that a good estimation of the noise and interference level can be obtained from the "channel-free" IFFT samples. Since LCPe can be significantly larger than the regular CP length (denoted as LCP) used in an OFDM system (for non-OFDM that does not define a CP length, the duration of a regular CP, or LCP, is often chosen based on the excessive delay spread of the channels encountered in a deployment, as discussed before), the allowed Nsh can be significantly reduced. To improve the number of shifts available for other non-initial ranging functions, the initial ranging can be confined to a certain number of (say Nbl’) sub-bands on which the allowed number of shifts is, only for example, Nsh’=aNsp/ LCPeÌ-1. But on the remaining Nbl-Nbl’ sub-bands, where only non-initial ranging is allowed, the number of shifts can be increased to Nsh=aNsp/LCPÌ-1. Often, the total ranging opportunities increases. If initial ranging is allowed on only Nbl’ (