Cisco Systems 7920 manual Minimum Requirements for Wipt Cells, Strength Minimum SNR

Chapter 1 Overview

Recommendations for Successful VoIP Surveys

Figure 1-2 Signal to Noise Ratio

Minimum Requirements for WIPT Cells

Table 1-1lists the minimum values for voice and data cells. For WIPT cells, Cisco recommends that the cell edge be –67 dBm and the SNR be 25 dB using a data rate of 11 Mbps. These values are much more restrictive than those needed for data because of the sensitivity to delays and retries for voice clients.

Table 1-1 Minimum Signal Strength and Signal to Noise Ratios for Voice and Data Cells

	Data Cell		WIPT Cell
	Minimum Cell		Minimum Cell
	Edge Signal		Edge Signal
Data Rate (Mbps)	Strength	Minimum SNR	Strength	Minimum SNR
54	–71	25	—	—
36	–73	18	—	—
24	–77	12	—	—
12 or 11	–82	10	–67	25
6 or 5.5	–89	8	–74	23
2	–91	6	–76	21
1	–94	4	–79	19

Figure 1-3shows how the difference in transmit powers between the access point and the WIPT client creates different effective ranges. The 5 mW signal probably would continue all the way to the access point, but if the access point antennas do not have enough gain to make up the difference in received signal of the WIPT client, then the WIPT packets will not be decoded. A high-gain antenna on an access point will receive a signal from a 5-mW client from a greater distance than a low-gain antenna. It is the

Site Survey Guide for Deploying Cisco 7920 IP Phones

1-4 OL-6315-01