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Publication Number: 543300 Rule Parts: 15.247 Publication Date: 02/12/2009
Keyword: Section 15.247; Point to Point versus Point to Multipoint

First Category: Radio Service Rules
Second Category: Part 15 Intentional Radiators

Question:   An RF system employs a central access point transceiver that communicates with multiple user stations simultaneously. Transmission of data from the access point to user stations is accomplished through code division multiple access (CDMA). The access point transmits one carrier on which multiple pre-ordained data streams are separated through imbedded code division. The system does not intentionally broadcast where two or more remote stations receive the same information (except for internal system management), or if two users select the same multicast traffic (multicast is independent of the system and a feature of the internet). The system described is multiple point-to-point links between the access point and a user station. This is therefore considered a point-to-point application, and permitted a 1 dB reduction of power for every 3 dB of antenna gain over 6 dBi (which is permitted under Section 15.247 (4) (i) for point-to-point operation in the 2400-2483.5 band).

1. If a similar RF system was instead transmitting to multiple users using time division multiple access (TDMA), would it also be considered point-to-point since it would not be simultaneously transmitting, and would only be transmitting to one station at a time?
 
2. In the case of both systems above, are the remote users considered point-to-point or point-to-multi-point, and can the 1 db of reduction for every 3 dBi of antenna gain over 6 dBi be applied to both systems?



Answer:   1. No, the proposed systems (CDMA and TDMA) are point-to-multipoint systems, subject to the +36 dBm EIRP maximum limit. The systems are transmitting to multiple users. From the perspective of interference potential, it makes no difference that the signals are multiplexed and each remote station can distinguish its intended data in the receive signal. However, point-to-multi-point systems in the 2400-2483.5 MHz band that employ multiple directional beams directed to individual user stations may be permitted a 1 dB reduction of power for every 3 dB of antenna gain over 6 dBi. These systems must comply with all the pertinent provisions in Section 15.247(c)(2).

2. The remote users are considered point-to-point and can therefore take advantage of the power reduction rule for point-to-point systems under Section 15.247(c)(1).

 



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