IEEE is a numbered style with two components:
In-text references where references are numbered  in the order of appearance in the article. See examples Fig.1. and Fig.3.
A reference list, displayed at the end of the article which provides full details of all references cited in-text. The references are ordered as they appear in the in-text references (in order of citation, not in alphabetical order). See examples Fig. 2. and Fig. 4.
For further information, please refer to the guidelines on IEEE Documentation Style from the Institute of Electrical and Electronics Engineers site.
Using this system, references are numbered in the order in which they are first cited in the text. If the same reference is cited later in the text, the same number is given. For example
"The theory was first put forward in 1987 "
"Scholtz  has argued that......."
"Several recent studies , , , ,  have suggested that..."
, ,  [1, 3, 5]
 -  [1-5]
If you need to cite the same source more than once:
Direct the reader to specific pages numbers where necessary, for example, a quote, or specific sections of the reference you wish to highlight such as tables, figures, algorithms:
...see [12, Example 1].
There are two different styles of referring the reader to in-text references: one way to do it is called "author prominent", the other way is "information prominent". You should consider your readers' needs, or which is most relevant when deciding which method to use. The two different styles are detailed below.
Information Prominent In-text Citations and Corresponding Reference List
Fig. 1. Information prominent in-text references.
Fig. 2. Reference list excerpt corresponding with in-text references in Fig. 1.
The full article for Fig.1. and 2 can be retrieved from:
|||S. R. Bhaskaran, S. V. Hanly, N. Badruddin, and J. S. Evans, “Maximizing the sum rate in symmetric networks of interfering links,” IEEE Trans. Inf. Theory, vol. 56, no. 9, pp. 4471–4487, Sep. 2010. doi: 10.1109/TIT.2010.2054652|
Author Prominent In-text Citations and Corresponding Reference List
Fig. 3. Author prominent in-text references.
Fig. 4. Reference list excerpt corresponding with in-text references in Fig. 3.
The full article for Fig.3. and 4 can be retrieved from:
|||X. Li, J. Vucic, V. Jungnickel, and J. Armstrong, "On the capacity of intensity-modulated direct-detection syst. and the inform. rate of ACO-OFDM for indoor optical wireless applications," IEEE Trans. Commun., vol. 60, no. 3, pp. 799-809, Mar. 2012. doi:10.1109/TCOMM.2012.020612.090300|