{"id":130,"date":"2011-06-20T11:54:16","date_gmt":"2011-06-20T11:54:16","guid":{"rendered":"http:\/\/www.raymaps.com\/blog\/?p=130"},"modified":"2011-08-23T05:52:48","modified_gmt":"2011-08-23T05:52:48","slug":"wcdma-capacity","status":"publish","type":"post","link":"https:\/\/www.raymaps.com\/index.php\/wcdma-capacity\/","title":{"rendered":"WCDMA Capacity (Mbps)"},"content":{"rendered":"

The capacity of any wireless communication channel is given by the well known Shannon Capacity Theorem:<\/p>\n

C=B*log2(1+SNR)<\/p>\n

or<\/p>\n

C=B*log2(1+P\/(NoB))<\/p>\n

where C is the capacity of the channel in bits\/sec, P in the noise power in Watts, No is the noise power spectral density in Watts\/Hz and B is the channel bandwidth in Hz. It is obvious that the channel capacity increases with increase in signal power. However, the relationship with bandwidth is a bit complicated. The increase in bandwidth decreases the SNR (keeping the signal power and noise power spectral density same). Therefore the capacity does not increase linearly with bandwidth.<\/p>\n

\"\"<\/a>
Single User Capacity<\/figcaption><\/figure>\n

It is assumed that the signal power is -80dBm and the noise power spectral density is -170dBm\/Hz.<\/p>\n

Let us now consider the case of a WCDMA system where the noise component consists of the AWGN noise as well Multiple Access Interference (MAI). The above capacity formula is then modified as:<\/p>\n

C=B*log2(1+SINR)<\/p>\n

or<\/p>\n

C=B*log2(1+P\/(NoB+(U-1)*P))<\/p>\n

where U is the number of users.<\/p>\n

\"\"<\/a>
WCDMA Capacity<\/figcaption><\/figure>\n
\n
<\/dl>\n<\/div>\n

It is assumed that WCDMA system has a bandwidth of 5MHz, signal power of -80dBm and noise power spectral density of -170dBm\/Hz. It is observed that the capacity of the WCDMA system decreases exponentially with increase in number of users (all users are assumed to have equal power at the receiver). The capacity of a 5MHz channel drops from about 38Mbps for a single user to about 370kbps for 20 users (the combined capacity of 20 users is 7.4Mbps which is much lesser than the capacity of a single user in AWGN only).<\/p>\n

Note:<\/p>\n

1. In some references the signal power is adjusted by the processing gain but I think that this is not correct for capacity calculations because in that case the bandwidth should be adjusted as well.<\/p>\n

2. The capacity in fading environments would be less than AWGN capacity. However, multi-antenna systems allow for higher capacities.<\/p>\n","protected":false},"excerpt":{"rendered":"

The capacity of any wireless communication channel is given by the well known Shannon Capacity Theorem: C=B*log2(1+SNR) or C=B*log2(1+P\/(NoB)) where C is the capacity of the channel in bits\/sec, P in the noise power in Watts, No is the noise power spectral density in Watts\/Hz and B is the channel bandwidth in Hz. It is obvious that the channel capacity increases with increase in signal power. However, the relationship with bandwidth is a bit complicated. The increase in bandwidth decreases the SNR (keeping the signal power and noise power spectral density same). Therefore the capacity does not increase linearly with […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[22,16],"tags":[32,26,29,113],"class_list":["post-130","post","type-post","status-publish","format-standard","hentry","category-capacity","category-wcdma","tag-shannon","tag-sinr","tag-snr","tag-wcdma"],"_links":{"self":[{"href":"https:\/\/www.raymaps.com\/index.php\/wp-json\/wp\/v2\/posts\/130","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.raymaps.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.raymaps.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.raymaps.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.raymaps.com\/index.php\/wp-json\/wp\/v2\/comments?post=130"}],"version-history":[{"count":16,"href":"https:\/\/www.raymaps.com\/index.php\/wp-json\/wp\/v2\/posts\/130\/revisions"}],"predecessor-version":[{"id":353,"href":"https:\/\/www.raymaps.com\/index.php\/wp-json\/wp\/v2\/posts\/130\/revisions\/353"}],"wp:attachment":[{"href":"https:\/\/www.raymaps.com\/index.php\/wp-json\/wp\/v2\/media?parent=130"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.raymaps.com\/index.php\/wp-json\/wp\/v2\/categories?post=130"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.raymaps.com\/index.php\/wp-json\/wp\/v2\/tags?post=130"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}