{"id":940,"date":"2011-10-28T07:38:56","date_gmt":"2011-10-28T07:38:56","guid":{"rendered":"http:\/\/www.raymaps.com\/?p=940"},"modified":"2011-11-17T05:57:24","modified_gmt":"2011-11-17T05:57:24","slug":"lte-resource-allocation-in-time-frequency-plane","status":"publish","type":"post","link":"https:\/\/www.raymaps.com\/index.php\/lte-resource-allocation-in-time-frequency-plane\/","title":{"rendered":"LTE Resource Allocation in Time-Frequency Plane"},"content":{"rendered":"

The LTE standard defines a resource allocation structure in time and frequency domains. If the spatial domain is also considered the resource allocation structure actually becomes a 3-dimensional arrangment. We will ignore the spatial domain for now and focus on the time-frequency plane.<\/p>\n

In the time domain the LTE transmissions are organized into frames of 10 msec length. Each frame is composed of 10 subframes of 1 msec duration. Each subframe is made up of two equal sized slots of 0.5 msec each. Each slot is composed of 7 or 6 OFDM symbols depending upon whether a short or long Cyclic Prefix (CP) has been used. In the case of a short CP the CP has a duration of 5.21 usec for the first symbol and 4.69 usec for the remaining 6 symbols such that the total slot duration is 0.5 msec. For the long CP the CP has a duration of 16.67 usec for all 6 symbols. The useful symbol duration is fixed at 66.67 usec.<\/p>\n

Short CP
\n1*(5.21+66.67)+6*(4.69+66.67)=500 usec<\/p>\n

Long CP
\n6*(16.67+66.67)=500 usec<\/p>\n

\n
\n
\"Frame<\/a><\/dt>\n
Frame Structure for Short CP<\/dd>\n<\/dl>\n<\/div>\n

In the frequency domain the subcarriers are spaced at 15kHz giving a useful symbol duration of 1\/15000=66.67 usec after the IFFT operation. A group of 12 subcarriers (12*15=180 kHz) over one time slot (0.5 msec) is referred to as a Resource Block (RB). With 1200 subcarriers available over a 20 MHz bandwidth the LTE transmitter has 100 RBs available over one time slot.<\/p>\n

The smallest unit of resource is termed as the Resource Element which is composed of one subcarrier and one OFDM symbol. Thus an RB has 12×7=84 and 12×6=72 Resource Elements for short and long CP respectively.<\/p>\n

Note:
\n1. The total number of subcarriers over a 20 MHz bandwidth is calculated as 20000 kHz\/15 kHz = 1333 subcarriers, which is much greater than 1200. This is because all subcarriers are not used and some subcarriers act as guard carriers at the edges.<\/p>\n

2. Longer CP is useful in environments with long delay spread.<\/p>\n","protected":false},"excerpt":{"rendered":"

The LTE standard defines a resource allocation structure in time and frequency domains. If the spatial domain is also considered the resource allocation structure actually becomes a 3-dimensional arrangment. We will ignore the spatial domain for now and focus on the time-frequency plane. In the time domain the LTE transmissions are organized into frames of 10 msec length. Each frame is composed of 10 subframes of 1 msec duration. Each subframe is made up of two equal sized slots of 0.5 msec each. Each slot is composed of 7 or 6 OFDM symbols depending upon whether a short or long […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[18],"tags":[73,70,114,71,72,74,69],"class_list":["post-940","post","type-post","status-publish","format-standard","hentry","category-lte","tag-frame","tag-frequency","tag-lte","tag-resource-allocation","tag-subcarrier","tag-subframe","tag-time"],"_links":{"self":[{"href":"https:\/\/www.raymaps.com\/index.php\/wp-json\/wp\/v2\/posts\/940","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=940"}],"version-history":[{"count":37,"href":"https:\/\/www.raymaps.com\/index.php\/wp-json\/wp\/v2\/posts\/940\/revisions"}],"predecessor-version":[{"id":1233,"href":"https:\/\/www.raymaps.com\/index.php\/wp-json\/wp\/v2\/posts\/940\/revisions\/1233"}],"wp:attachment":[{"href":"https:\/\/www.raymaps.com\/index.php\/wp-json\/wp\/v2\/media?parent=940"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.raymaps.com\/index.php\/wp-json\/wp\/v2\/categories?post=940"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.raymaps.com\/index.php\/wp-json\/wp\/v2\/tags?post=940"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}